Really? I generally have great results with Slurpuff, maybe Slurpuff didn't fit your team very well. Don't forget Slurpuff requires more team support than your conventional Pokemon. By the way, BD Azumarill is just as easily checked/countered and weakened as Slurpuff is (at least that's what I found when i used BD Azu and BD Puff). I kinda agree with you on the last part you said though, it's useable but generally outclassed.Alright, here we go.
Last night, I was up laddering using a Slurpuff, and I have to say, it's extremly nitche. Sub / Belly Drum / Drain Punch / Play Rough is probably the best way to go. Sure, it brings you down to 50% health, but really, if you don't have a Sub up, most priority stops you. This allows you to take out an extra Pokemon while they break your Sub. However, you absolutely NEED to remove anything with priority, Scarfers, or moves that go through Subs at ALL COSTS. I've only gotten one sweep, and that was lower on the ladder since I was using an alternate account. I guess it could be decent with the right team support, but why bother? Azumarill is much easier to slap on a team and doesn't require a lot of team building. Sure it's slower, but that's not as important as being hard countered and or weakened by so many Pokemon.
It'll probably be borderline, just because it destroys most of UU, but not worth using in OU. Just like Salamence (before Mega Mence), it's useable, but not really worth having it's own thread.
Also, aside from Talon's brave bird and Scizors and Megagrosses bullet punch, Puff can take most priority hits faily well.