Sorry, but I think you don't understand my point.
In other metagames, you have more than one pokemon. So, if Hoopa-U crits your Mandibuzz and kills it, you can, for example, revenge kill it with another faster pokemon or a pokemon that has access to priority like Pheromosa, Golisopod, Tapu Lele, Scizor... etc. Or you can abuse the momentum you gain after your critted mon faints to bring your own sweeper and set it up to strike back. So crits are definitely manageable and a single crit is rarely the reason for losing a battle.
In some rare situations crits can even be bad for the one who scored the crit. Example: Your opponent has a severely weakened Ferrothorn in the battle, you have a Scizor/Landorus/Pheromosa and use U-turn. Ferrothorn barely survives the U-Turn, you gained momentum and can now set-up your Charizard X, abusing the passivity of Ferrothorn. But when your U-Turn crits, Ferrothorn dies, meaning you switch out first, and lose all momentum to your opponent.
So, in a 6on6 there are multiple ways to handle crits, since a pokemon dying always means that you have the momentum and can make a "free" switch to another pokemon - but in 1v1 you have only one pokemon, so that a crit always means that the player who got the crit wins -> RNG decides the battle.
I also don't want to ban hax entirely, only crits are problematic in my opinion. Also, you aren't following the cartridge mechanics with implementing OMs like this, since there's no format in the cartridge games where players have teams of three pokemon and battle with one of them.
I can see what you mean about crits. Yes a critical hit can win or lose a match, but that's just how the game is. The chance of a critical hit is 1/16. The chance of high jump kick missing is 1/10. Ban high jump kick?
No, that's not happening, and neither will a ban on crits.