Azumarill on its own isnt deadly, but due to the doubles nature, once it sets up, it is really hard to bring down. Around 1/3 of my losses are because of being swept by this bunny. By all means, it should be Jirachi, its powerful partner that should have been banned, or the move belly drum, but as for this suspect, yes, Azumarill is really hard to predict at times, and can be broken if played correctly. So yes, I vote to Ban Azumarill.
In my mind Azu doesnt deserve to be banned since on its own it isnt too big of a threat even it does get up a belly drum in some cases. This is because several pokemon can check azumarill pretty easily some of these include Amoonguss, Kangaskhan, Virizion, Ludicolo and strong spread attackers that arent weak to aqua jet. What makes Azu feel broken is the presence of redirection users next to it for example Amoonguss, Togekiss, Volcarona and the biggest culprit Jirachi. But since were not suspecting these redirection users at this time my previous points still stand.