> pretty loyal Pokemon fans despite being in their 30's

Pokémon is 28 years old, so people now in their 30s would have been the core demographic of Pokémon fans at the start. I would expect them to be the most loyal fans, no "despite" needed.

> How is this any different than Digimon?

The criticism I've seen is of specific creature designs that look very close to those of specific Pokémon. I don't particularly care about that either – but the criticism is not just that it's another mon collection game.