Not a lot of people use her for the acu or poison thou, and those two certainly aren't reliable. The acu usually only matters if enemy only have a single debuff layer remover (most people run full or 2 debuff removal, if any). And only water main care for the poison, as they are the only one that can stack it to anything useful(as long as pile on enough other debuff&cc to make them *, as poison have low removal priority)
She does have downfall in being somewhat reliant on her barrier. Her chakra cost is middle of the road @60, which is actually mildly awkward. And finally, she doesn't chase her own mystery, which means that you can "interrupt" her work by CCing her OR another ninja, which makes countering her much easier
That said, she is one of the most versatile rare tier ninja, perhaps only danzo matches her as far as versatility is concerned. I do find it laughable that people keeps bringing the 25% anti-male thing up thou, she doesn't actually hit all that hard, not even against males, especially not her mystery if you consider that it's a 60 chakra cost mystery (which, btw, also have the issue of having largely random targets). Her mystery damage is only good if the ignition *s, so talking about her damage AND about her ignite as if it's two separate "power" is silly. Granted, that might be different if more buffs are stacked to boost her damage, but that's kinda true for any ninja. My wind team (I'm wind main) deals by far more damage then the team I have mei on, thou the team I have mei on is my preferred PvP as it's more versatile and less likely to be countered.
To be fair, if there will be "adjustments", mei is more likely to be nerfed than many others. But people are most certainly exaggerating the problem here.
in my merge server, 65% they use mei, with water style, fire style, that is really good:funk: