Firstly, Liepard teams are NOT easy to disrupt even if you see it coming right from the start. Here are a few ways you could theoretically disrupt these teams with: Cradily, Kangaskhan, Magic Coat users, double switching with your Stealth Rock user. However, these Pokemon cannot find their way on every team, but even if they do, smart playing by the Liepard user can get around all of them: The Liepard user could, for instance, shuffle around the opponent's team until the hazard user comes into play. From there, it is a losing situation for the opponent because if he double switches to try and catch Ditto, he risks giving Liepard a setup opportunity, and if he doesn't, he risks Ditto laying hazards on him.
Yes, there is no 100% way to win a Pokemon battle. You will have to predict, make appropriate plays, etc. in order to win.
I mean, honestly. Is this your argument? Smart play by someone using the team will give them the win? Smart play SHOULD yield you the win; that's how the game is USUALLY won. Making that sweet Nasty Plot setup, sub, or the switch predict means that you've outsmarted your opponent; you get the reward of advancing your win condition. If you want to eliminate these risks from a Pokemon battle, you are making the game milquetoast and unenjoyable to play.
This is literally almost risk free for the Liepard user because this shuffling can be done many times. ... Liepard forces Cradily users to use Suction Cups, which is completely inferior to Storm Drain, and every time he switches to Cradily, he again has to play that game of "will Ditto switch in?"
It can be done 32 times. You simply must lay down the rocks before using half of Assist's PP or you will often not have the gunpower to take down an opposing team. If you take too long to get to your win condition, you definitely have little to no chance of winning.
Suction Cups is actually common on RestTalk Cradily, a set which also does not run Stealth Rock; it's an absolutely viable set in NU and has more uses than defeating a Liepard.
Saying that smart play = a win is not an argument that leads towards a liepard ban; it's an argument that leads towards the opposite conclusion. In the game of Pokemon, you teambuild with checks, counters, and resistances in mind; viable counters to Liepard have more than one use (Kangaskhan is a great attacker, Cradily walls, pivots, sets up and sweeps, Magic Coat deflects hazards and defeats walls like Alomomola, et cetera, et cetera.)
If you look at metagame balance with your mindset, the game gets overcentralized, predictable, and boring. Your post does not tell us why the strategy isn't fit for competitive play, it tells us why the strategy is good.
EDIT: Not gonna double post again, but some things I missed;
"If you want to counter Liepard, your options and playstyle are very limited and one mistake in the game could very well screw you, while the opponent really doesn't risk anything apart from Liepard or Dirto dying."
Liepard and Ditto are the team's win conditions. Risking one of those two dying is risking your entire win condition, so it's basically risking the entire game on one play. If you want to be ballsy and predict the Sawk, you go for it, and you win if it pays off.
I'm glad that you agree that Assistpard isn't uncompetitive; it's good that some of our players approach these things with a more objective mindset. You have a point about Snow Cloak and Sand Veil which slipped my mind -- I'll admit that they effect the game in a bad way, but I'm sure we can agree this strategy is not to be banned for the same reason that these abilities were banned.
Kangaskhan CAN be tricked the flame orb; it's something that the player will have to take into account while playing. If the poke gets burned after your fake out, should you stay in and poke, or switch out? The choice is the player's.
If you think these counters are not splashable in a good NU team, then I have failed to convince you; it's entirely subjective and more wordfighting isn't going to convince you that any of these counters are practical. I won't bloat the thread further going back and forth, so this is probably my last post in the thread. That is the player's decision.