if azumarill was not relevant in the format or if he wanted it would be ou, and maybe blaziken and gyarados have a similar speed but about 3 points in speed can make a difference and remember that to carry sword dance and thunder puch would mean no protection, so They can easily defeat in one turn and if you wear sword dance and protection this will be left with little coverage. Pkmn like hawlucha which also has sword dance and you can double the speed with a partner or using the dynanax is not banned, but blaziken if because they do not know how to play against it and how they do not dare to lower it from ubers they can not know how to would adapt to the meta.You can run Swords Dance instead of Protect, seeing that Gyarados and Blaziken are almost identical speed, at the end of the turn Blaziken would have +2 Attack and +1 Speed. And you rightfully mention Thunder Punch, as that allows it to hit most of the Bulky Waters supereffectively, snipes Gyarados, and snips things like Mega Charizard Y. I do not know why you think its weak since its main draw is hitting what its weak to it and setting up Terrain. Bringing up Thunder Punch only cements this Pokémon as a broken mon in a dynamaxmetagame that should not be unbanned. Besides, even if it doesnt run Thunder Punch and subsequently has problems handling Guarados, does that mean that its balanced? I find your reasoning troubling, especially since you bring up Pokémon like Azumarill which are simply not relevant in Nat Dex.
even if they could try to prove it in ou and if it is extremely strong they ban it.