Going purely off of the profiles, I'm going to need to hear the explanation behind Charmander's range being "hundreds of meters with most attacks" because I doubt that.
It would give Charmander the edge at a distance, though. Plus this Charmander has its full learnset which means its fought many battles, so its experience shouldn't be underestimated. Most of Cuphead's experience comes from fighting opponents who tower over him, but Charmander is actually smaller (60 cm vs 91 cm) so Cup won't be landing as many hits as he would against those bosses.
That being said, Cuphead's superior mobility options and more varied ranged arsenal should be a big problem for Charmander to deal with as I can't think of any solid counters the latter has in terms of raw abilities. Plus, Charmander is only about 7% stronger and remember that's at most, so it's likely Charmander could be slightly weaker. I think Cuphead's Invinvibility powerup is pretty game-changing, too, as it would allow him to phase through all of Charmander's attacks while racking up damage much more easily, and certain charms will let him use it quite a bit.
I think I'm leaning towards Cuphead with high difficulty.
