M2 seems very solid against the trend of MK Wolf Diddy all getting extremely popular
MK and Diddy, yes. Wolf somewhat less so, but it's doable.
odd chars that don't feel so combo-food for him
That's really not a thing.
I would argue that he wins the Link matchup, though Tink can be troublesome.
If you want to beat a proficient Mewtwo, you need to fully cover the space between HC fair range and max range dash->Teleport/TeleAC range without exposing yourself to attacks from another position (most often the space directly behind you),
and you have to mitigate his typical survivability advantage. Tink and Wolf have flexible, noncommittal tools that extend into the midrange space and confirm into strong floaty punishes/kill confirms, adequate control of their own space, and they're mobile enough that Mewtwo can't easily outmaneuver them until he can create an advantaged position. Lasers are difficult to counteract effectively (limited laser lifespan works in Wolf's favor here), and Tink's bombs are somewhat resistant to his usual strengths in item play (shield->WD catch doesn't work reliably and he can't swat them unless you're willing to commit to a tipper utilt, plus Tink likes to throw from positions that are difficult to react to in time for a raw WD catch). Even so, if Mewtwo gets a read or the opponent is pushed into a situation where they can't utilize those tools effectively then Mewtwo can get a lot of mileage off of that opening.
Most characters run into some issue or combination of issues in the Mewtwo matchup wherein they're unable to adequately contain him, get outboxed in close quarters, can't keep up and thus give him too much opportunity to charge Shadow Ball, can't kill him, get bullied too hard in punishes/edgeguards, etc. If few enough of these things hold true then you can potentially argue for an evenish matchup given sufficient strengths in other areas, otherwise you're probably in for a bad time. Link for example is slow, loses at midrange (boomerang is easy to navigate around) and risks getting outboxed by Mewtwo's stronger close-quarters pressure, can't reliably kill (dthrow->dair isn't real), and gets wrecked by corner carry into edgeguards. He does have tools that can work in this matchup, but he has to work harder and play better to keep up with Mewtwo.
Even if say oddball stuff like Zard hangs around in PM meta, I feel something like that would be a bigger hindrance to Mewtwo viability than the Meta being essentially 6 chars, since the other 5 would likely be extremely tasty for him to to combo to death from fairly minor mistakes (3 spacies, MK, and Diddy)
Zard is jokes. His movement is equal or worse in pretty much every metric (Mewtwo arguably has a better dashdance, despite what Zard's higher dash/runspeeds might suggest. Zard's bulk is an issue, whereas Mewtwo's dash is fairly generous in terms of hurtbox displacement), he can't reliably confirm elevator combos on Mewtwo, and he gets fat shamed into free edgeguards very easily. If I was to point to somewhat annoying oddballs (ie still even at worst imo), it'd be the likes of Pikachu and maybe Squirtle.