Grandmaster Mei main here. I’d like to dispell some of the blatant misinformei-tion about Mei that is often spewed around these forums.
1. "Mei should be reworked!"
Just because you don’t like a certain hero doesn’t warrant a rework. By the same logic, Doomfist, Junkrat, Widowmaker, Genji, Brigitte etc. should all be reworked if we’re going by the same philosophy (since they have proved time and again to be the most hated heroes in the game)
2. "But I can’t counter Mei!"
Mei’s hero design and playstyle is one that preys on the kinds of mistakes that people at lower ranks often make. It’s not that she’s OP, it’s that you’re simply not good enough. I know that people don’t like being told when they’re bad at the game, but hero balance should not care about your feelings in this way.
Additionally, there ARE heroes who counter Mei. Pharah, Doomfist, Widowmaker, etc can all be a nightmare for Meis on more open maps with better sight-lines. This is not to say that they are HARD counters. On certain maps, you will have a hard time dealing the Mei simply because that map favours her. All heroes have maps that favour them more so than others. Deal with it.
3. "Ice wall is too OP on certain maps!!!"
Ice Wall recently received an unneeded nerf in which its HP was lowered from 500 to 400, and as a compensation ‘buff’, Mei’s primary fire received a slight damage buff (this damage buff is of no significance in any way, so this change was overall quite a heavy nerf).
Additionally, not all Ice Walls are equal. Most Meis tend to waste their Ice Walls, either because they always miss/don’t realise opportunities for good walls, or they simply have a high rate of error with their Ice Wall placement. I guarantee that you only notice these things when you’re against… oh you know… someone who’s actually GOOD at Mei?
4. "Freeze is unfair it should be removed!"
Mei’s freeze is the only non-immediate stun ability in the game. All other stun abilities will perform their stun as soon as they hit. (Case study: Eartshatter, Rocket Punch, Flashbang, Shield Bash, Hog Hook, etc.)
Against an actual coordinated team, a Mei will often have to exhaust all their cooldowns to achieve 1 freeze due to her relatively slow time to freeze enemies (she has to use cryo-freeze to bait out enemy stuns and burst damage, and uses Ice Wall to single-out targets). This is the point at which you focus the Mei to kill her, because she is at her most vulnerable. Part of a coordinated team is realising these weaknesses, and when to push to exploit them.
TLDR; there is a tonne of misinformation about Mei on these forums and elsewhere. Mei is currently in a very balanced state. She is powerful when used correctly, but at the same time, the threat of an enemy Mei can be greatly controlled with actual coordination.