Convergent mons suck for the opposite reason regional varients suck, though both come from the same root cause/issue.
Gamefreak clearly sees them just as opportunities to make "X pokemon but Y type", not actually examples of regional adaptation or convergent evolution, most convergent mons and regional variants undermine the entire implied ecology they're ostensibly intended to evoke with their dex entries and the like.
Actual regional forms would be shit like different patterns of stripes on Arcanine alongside slightly different proportions, or differently shaped horns and bone armor on houndoom, etc. Not "Sandslash but his spines are now magically made of ice and they live in tundra even tho there was a desert they could have lived in anyways" (and no, the volcano/earthquakes isn't an excuse, they could have adapted to a more temperate area instead of the fucking ice caps)
Likewise, Convergent mons would be stuff like
>>53679391 or
>>53681707 , which still at least somewhat resembles their own organisms. Technicallyt that's more mimicry then convergent evolutions as
>>53680761 says, but at least they still look somewhat like their own mon wheras wigglet is almost identical to diglet.
If GF wants to do "X mon but with Y type", they should have explained it via random mutation from radioactivity or something supernatural or like it coming from a parallel dimension/timeline.
They also all suck because GF, again, clearly sees them as a way to "revisit" older pokemon and since Regional varients change so much about the original mon, there's like an 80% chance that you won't even like the variant and you get cucked out of a proper evolution or mega that would have actually iterated on what you liked about the original mon.
