I disagree. While Shadow Tag can be executed by both players as being 'the best strategy', the issue is even both players use Shadow Tag, it doesn't mean the game is 'fair'. In fact, the outcome of the match will depend on the matchup between the Shadow Tag teams. I will illustrate it with an example.Alright so I am actually going to help shrang out as I feel he's having to fight a one-man war against Melee Mewtwo and everyone else, and he has actually managed to change my opinion from viciously pro-ban.
Personally I think that all this throwing around of the word "uncompetitive" is a load of rubbish. The premise of Shrang's argument is that Shadow Tag can be built around and can be used by both players, so you cannot really say that it is "unfair" because both players have access to it. If one player brings Kyogre / Arceus / Xerneas and the other brings Deoxys-N / Garchomp / Gardevoir, then the player with the less overpowered team cannot complain about his opponent having the advantage as he too can use Kyogre / Arceus / Xerneas. The tier is unbelievably centralized and that's not been a problem, so saying that Shadow Tag is centralizing is no good because you CAN prepare for it. You can argue that you can prepare for it and still lose, but isn't that true for so many things? You can bring your Giratina-Origin / Scizor core to cover yourself against Extremekiller and then lose to Fire Blast / Shadow Claw, for example. You can bring your sturdy Klefki along then get sniped by Xerneas once or twice and suddenly you can't check it anymore (or you can lose to Xerneas that run specific investment to make Substitutes unbreakable by Play Rough).
Something else that I think Melee Mewtwo is not realising or not admitting is that the "you can prepare for it but lose to it anyway" works in both ways. Let's go through the different methods of dealing with Shadow Tag:
Punishment Arceus - loses to Charm Gothitelle. But what if the Gothitelle is Trick Room or Heal Bell? you can contently let them get to +6 then snipe them with Punishment. "But I prepared my Gothitelle for Support Arceus with Taunt!". Too bad, you lost your Shadow Tag user.
Roar Arceus - loses to Taunt Gengar and Taunt Gothitelle. But what if the Gothitelle is Charm? you contently let it Charm you to -6, then smile as you Roar it away as it goes for Calm Mind number 5 or 6. "But I prepared for Punishment / Poison Jab / Waterfall / whatever Arceus with my Gothitelle!" Too bad, you can do nothing.
Earthquake 176+ Arceus-Grass - loses to Gothitelle (unless you run Bullet Seed and it doesn't have Charm), but outspeeds and surprise KOes Gengar. "But i prepared for Grassceus by adding Gengar to my team with Scarf Kyogre and Specs Palkia!" yeah well you got sniped by Earthquake, sucks to be you.
"But I don't want to run shit moves on my mons so that I don't lose to Shadow Tag!" Yeah well I don't want to have to run Palkia on 70% of my teams so I don't lose to Scarf Kyogre. I don't want to run Steel-Types that suck ass just so that I don't lose to Xerneas. I don't want to run Thunder Wave Palkia to insure myself against Xerneas. But I HAVE TO because Ubers is and always has been a tier that is CENTRALIZED. You can argue about being forced to run X mon for Y, or A move for B mon, or not being able to use X Y or Z because Xerneas sets up all over them, but that has never been an issue. Like Minority Suspect said, if we have to run Defog Arceus-Ghost on every team alongside Shed Shell Palkia, then that's how it will be.
Also, arguing that "well all these moves like Thunder Wave Kia also come in handy against Support Arceus so that you can outspeed, Klefki can also set up Spikes and Prankster Twave a rampaging Blaziken, Scizor can also handle Extremekiller, you may be semi-forced to run these things but at least they don't ONLY insure you against Shadow Tag / whatever, and even then you can still lose!" Dragon Tail Kia can phaze out Calm Mind Arceus-Water and Calm Mind Kyogre, Earthquake Grassceus can get the jump on Dialga / Heatran etc.
All I know is I don't complain when I prepare for Extremekiller with Giratina-Origin and then I get smacked by Shadow Force, or when I run Arceus-Ghost and lose to Refresh Jolly Extremekiller. I think what some people need to admit is that they are using "uncompetitive" as a fancy word to hide what they truly want Shadow Tag banned for - Shadow Tag turns games into a bag of dicks, ruins the ONLY element of the game that we play it for - TO ENJOY OURSELVES. I know I don't enjoy Gothitelle slowly maneuvering during 40 turns so that it can get 4 Trick Room turns to sweep instead of 3, and making sure that it's at 90% health instead of 80% health when it kills the Support Arceus. I also despise the way that Gengar can snipe something that otherwise runs a train over my opponent's team because oh look, it Taunted my +6 Arceus as I tried to dodge Destiny Bond and now it can cheaply KO Arceus without any repercussions, taking away the fact that I outplayed my opponent and exposed a flaw in his teambuilding that meant he lost 6-0 to Calm Mind Arceus-Water. Not a SINGLE person can honestly argue that they enjoy playing against Shadow Tag, and I challenge anyone who thinks that Shadow Tag leads to a positive metagame that is made better by Shadow Tag's presence to speak up and post right here explaining why they think so. Right now I am still pro-ban, but not because I think it is "uncompetitive" or "removes choice" or bla bla whatever. I want it gone because I think it is poisoning the Ubers tier, and once it is gone I will be able to enjoy all the Ubers matches that I play, which thanks to Shadow Tag doesn't happen right now.
Assume two players are against each other and both of the teams are carrying Stag. Team A uses Charm Goth and Team B uses hp fire/icy wind/taunt/d-bond MegaGar. When they have played for a while, they have clearly spotted their win condition. Player A can trap the GrassCeus in team B to let its ScarfOgre clean up while Player B can trap the opposing Mega Scizor and allow its Ekiller to sweep. Both of them realised to prepare for Stag in teambuilding in order to not let their checks to dangerous mons be trapped and killed by Stag. Team B's GrassCeus is using Bullet Seed(yeah, I'm using it now) while Team A's Mega Scizor is using a wierd ass SpDef Occa Berry set with Knock Off. Both of them have 'prepared' for Stag but it's obvious that Team B's trapping won't be successful. Player A will therefore have an inherent advantage over Player B regardless of the skill of both players and quality of both teams thanks to Shadow Tag.
The issue of Shadow Tag is 'You can prepare for it, but your way of preparation won't necessarily work. Ultimately, the player with the right preparation to the specific opponent's Stag's set will have an inherent advantage. This turns the Ubers tier into a matchup-based metagame due to Stag limiting the important mechanics of switching'