"Not viable" means just that: it is not viable in the general metagame and therefore weighs down the team in all but a very small number of situations. Something doesn't become viable just because it ostensibly helps against one playstyle.
I've never played SF4, but imagine there was a fighting game where nobody could see which character the other person chose until the match started. There are a bunch of well-rounded characters with various strengths and weaknesses. But then there is a character called S, who sucks against all those characters for some reason (he's slow, not as strong, his attacks are too punishable, whatever). Then there is a character called P, who is really powerful and can dominate against every character--except S who for whatever reason has an even matchup vs. P.
In that situation, P is still overpowered, and S still sucks. P can still win every time against the dozens of normal characters, and S still loses against them. Only in one situation is S useful to the player, and otherwise in almost every other circumstance choosing him is a huge liability. Telling people to "just deal with P by picking S" means you're telling people they have to choose between always losing to normal characters, or always losing to P.
Or we can just tell everyone to pick P. But then there goes any variability to the game (which people will whine about anyway).
What we want for a metagame, is one that is both as skill-dependent and as diverse as possible without changing the core game mechanics. When one type of team can steamroll through everything except teams that have a few things that suck against other types of teams, you lose both of those things: skill-dependency because the game becomes overly matchup dependent (gimmicks > OP strategy > normal teams > gimmicks), and diversity if people gravitate to the OP strategy in hopes of winning lots of matches and actually standing a chance vs. others using the strategy.
Pokemon is matchup dependent to a degree no matter how you look at it, of course, but when the game becomes essentially a rock-paper-scissors thing where the game is over at the battle preview, that doesn't exactly sound fun. And trying to balance the game to avoid that certainly isn't lazy.
Tl;dr for the above: Regardless of what anyone thinks about whether BP is (still) overpowered, I really wish this type of "just deal with it" argument would go away. If BP isn't broken, then there's nothing to do about it. But if it is, then that needs to be addressed. The problem with saying "just deal with it" is that it avoids such questions completely. Smogon is trying to balance the 6v6 singles metagame; anyone who does not like that philosophy as a whole (rather than just individual decisions) would probably have a better time just playing on battle spot under Nintendo's rules or with friends using their own rules, rather than trying to tell Smogon to stop doing what it was made to do.
It's easy to just shout out supposed solutions and go "lol u guys are dum," but if they are unconventional or have been shown to be poor choices in the past, nobody will take them seriously until we see those things in action not only against BP teams, but also vs. the metagame generally.
To address Psych Up specifically, the issue is simply that the move is dead weight against everything except BP chains.
Perish Song is more useful generally, but the only OU-viable pokemon to get it (which means, the only pokemon that can do well in OU generally, including outside of going against BP teams) is Celebi. Politoed can also do it, but he is mostly dead weight outside of rain teams. Also, nobody in their right mind will ingrain before any potential perish song users are dead, especially with the current anti-BP vs. anti-banning firestorm encouraging to run Perish Song on things that wouldn't otherwise run it.
EDIT: Typo.
That is exactly what I am saying, things are unviable until something makes them viable and vice versa. Rotom is viable because it checks a lot of the top threats. If Perish Song > BP Teams, would Perish Song still be not competitively viable? One move on a popular Pokemon in order to take out an entire strategy sounds like it would be well worth it. You don't even need to trap, just force the switch and now 3 of his 6 Pokemon are not that useable. 1 move, out of your 6 Pokemon to handle 3 out of 6 of his Pokemon (2 that have no attacks). Take one of the 3 Pokemon out and the BP strategy falls apart.
In Street Fighter they do blind picks. Usually the person tells a judge who they will use (online already forces blind picks). The only time you get to switch is if you lost the previous round. Also counter picks don't = a win. You are usually better off playing with your best character because Skill > Pick. Tiers are based off of current strategies. And like previously stated in the Metaknight vs Pikachu example, the lower tier character moves to a higher tier if it beats the higher tier character easily and often. High tier characters are usually also most frequently used which is why a non viable pick can become viable if it counters the top threat.
Tiers comes down to how well a character performs at the competitive level which really comes down to tournaments (in Pokemon it also includes the frequency of use). If almost everyone uses one team/character/strategy because it is the strongest, then what ever defeats that ends up moving up in the tier as a counter to the top level of play. Just like the Metaknight vs Pikachu example. Characters get banned in fighting games when they use different mechanics than every other character. Maybe they can't be stunned or have a move that shuts down every other character's approach like Akuma's Air Fireball in SSF2. In those cases there is no counter play what so ever and the only way to win is to use that character.
And tiers aside, Dhalsim is considered pretty average, yet he still wins bad match ups and places high in tournaments. He uses his strengths to zone and keep the other person out so they cannot set up their offense. If he messes up once, there is a good chance he lost, but at the same time, he shuts down so many people in the hands of a skilled player because they cannot get in on him in the first place. Most Dhalsim players don't like to play the typical way of rush down, if they were forced to play that way, they would lose.
If BP is broken, then why aren't more people having success with it? Get some more replays of random people climbing the ladder recently using only BP and getting higher than they would with a standard team. If only a handful of people are capable of using the strategy effectively to get to the top, then maybe they are just better or their brain works with that strategy better than the typical teams. That is diversity.
To say, "I don't want to use it because it is stale" is like saying you don't want to use Legendary Pokemon because they're boring. Play to win, and in the case, use BP, get to the top, THEN you have an example of how broken the strategy is. So far the only proof of this is people claiming to have won multiple games in a row using BP, have any of them gotten to the top?
And on the deadweight comment. You know what else becomes deadweight? All 6 of your pokemon because they cannot deal with BP.
Also here's something most people seem to not realize, "Jack of all trades, master of none". Just because your team is balanced, doesn't mean you deserve to win over someone who is specialized. This applies to other sports and even when looking for jobs in real life.
Where you're wrong is that Smogon bans stuff that's different and doesn't fit "The Metagame". Stuff gets banned because either A) it's unrealistic to expect people to find a method of handling it on every team (Mega Kangaskhan, Blaziken, Kyogre) or B) it lets worse players beat better players due to BS (Shaymin S flinch hax, no good way to handle evasion, Mega Gengar coming in and killing off whatever it wants). Stuff like that ruins creativity, which, believe it or not, isn't what we're trying to do here.
Psych Up is bad against every sweeper in OU, so it has exactly one purpose in stopping BP, and frankly it doesn't do that well at it either. Stored Power with enough boosts will blow straight through basically anything you want to try to go with, outside of Sash Alakazam or whatever special Dark type you'd like to bring to the party. Perish Song is much more realistic, but it's still hard to fit onto a team given that the usable mons that would run it are Celebi, who isn't great in this meta, and Politoed, who demands a very specific team to make it worthwhile.
On a more constructive note, Choice Scarf Switcharoo Klefki is adorable / fucking bullshit, being able to come in at any time and force a Scarf onto a core member of the team is quite useful. It isn't too bad at messing with other teams as well, works a little bit like Thundurus (less offensive power, but being able to force mons into one move or spreading paralysis, poison, and Spikes on the enemy team is worth something). Dragon Tail is another option on defensive mons now that Sylveon can't be a part of the chain, so long as you pack enough of a punch to break Subs and have a method of getting around Smeargle it'll work well.
So I am wrong? Shaymin S Flinch Hax is banned, but Paraflinch isn't? Ok, that makes sense.
And I know you like to argue any and all points, but let's keep this on topic. I don't want to go on a rant regarding the Mega Bans.
Psych Up, fair enough. It isn't the best, just an idea and would require creative thinking to figure out the best way to use it and sweep back, such as on a Dark type not weak to DG like Houndoom (Currently not viable) or Bisharp. And Perish Song is also available on Gengar and Azumaril which are both very common Pokemon. Like I said before, 1 move to shut down 3 pokemon/strategy = pretty darn viable. Especially if BP becomes a big problem and more than a handful of people run it.
And yes, Prankster item swaps is another way to shut down BP early on. I usually start my Noivern with Switcharoo Scarf since it cripples and out speeds many things. If the sub becomes the problem there is also
Infiltrator, Sound Moves, Hail, and Sandstorm.
I do not get where you are going? It sounds like you are just arguing to argue? You agreed with my comment on Den's skill and provided an option for dealing with BP. Were you mainly here to just say I was wrong on my opinion of the Smogon Bans?