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.

The buff bit applies to every ninja, so it's irrelevant.
Maybe 100% buff stacked from a few sources boost her lowish damage to high damage, but the same will boost a high damage mystery into deadly.
My wind team, for example, if it all goes without a hitch, c*most wipe an enemy of similar power by end of round 2 if they don't have heals/shield. Mei's damage is not anywhere near that. Of course, Mei team is better in terms of reliability due to a number of reasons, but as far as raw damage potential goes, Mei is certainly NOT a winner.

Mei's damage is only good if the target is male AND the ignition *s (or alternatively, if you consider the amount of healing denied on a heal-removal, which only pure cleanse, like gakido/dance, gets around).

And frankly, it's rather childish to just count the debuffs, only people who can't form actual argument would resort to counting things
I mean seriously, which is stronger:
apply chaos to all enemy
Or apply blind, paralysis, acupuncture, immobile to ONE enemy at the same time (so you can't split them)

The former is ONE debuff, and most people would consider that OP if it can be easily done. The latter? it's rather insignificant, while it certainly hard CCs ONE target, for all intend and purposes 2 of the debuff does nothing other than making cleanse more difficult.
Granted, Mei's debuff aren't as "useless" as that (thou tbh paralysis is probably better than that poison a lot of the time). But then again at least I'm not adding sleep to the list, since immobile and sleep are never applied together since they don't stack (nor chaos, which is MOSTLY stronger than immobile, but isn't 100%)

So in reality, you need to consider what those buff/debuff DO.

In Mei's case?
ignition + anti-male buff patches up her damage to be on par with other high cost jutsu nukes
immobile is her REAL reliable debuf
Acupuncture is a unreliable debuff, which gives a nice boost that brings her up to "rare" tier.
Poison does very little, just a bit "extra", which might put her slightly over rare tier, but not super rare tier

So do I consider her better than most rares? yes, yes I do. But by no mean is it excessive like some of you make it sound.

So stop just counting stuff, if that's your only argument, you have no argument. You need to actually think about what the stuff DO and form an actual logical argument from that.

What is your point then? 4 is just an arbitrary number, what LOGICAL reason do you have to say it's too many?
What are you going to complain about next?
The fact that Chiyo ten puppet have 6 chases when 3 is the maximal otherwise?
The fact that Hokage Tsunade can heal up to 12 targets when 9 is the maximal otherwise?
The fact that Sasori 100 puppet can summon 5-8 puppets at once when 4 is the maximal otherwise(btw, there is only one 4 and I think one 3, rest are 2s and 1s)?
At least Boss Hinata is not in the game yet, or maybe you won't like the fact that she causes 32 combo and chases 64 combo. (well, there is just one chase 20 right now, maybe you take issue with that too?)

You are complaining about some arbitrary number without actual logical reason to say WHY it is too much, that's not "thought" as it involves no thinking.

WHY is 4 excessive. You can't say something is excessive simply because it have more than others, there will ALWAYS be one that have the most (thou there might be ties)

P.S. I am actually somewhat surprised at the number of ninjas whose jutsu affects 9 targets.