The effort and production that have gone into this is amazing, its genuinely one of the most ambitious and well executed full conversion mods I've seen.
...But as someone who has obsessed about this specific idea for longer than this game has been in the works, man is the actual dex kinda underwhelming. I understand it's specifically for Alpharad, but there is definitely a bias towards the games he likes (there are like 12 TTYD guys and two of them are recolors, and the Jabbi line is a completely baffling choice), some mainline Mario games are just fully ignored (Mario Kart World has more representation of Super Mario Land than this fan game that could have included anything from the series, and there's nothing from Super Paper Mario). There are also some that are just kind of baffling choices in general, like having Podoboo and Lava Drop. There are really good ideas for some of the evolution lines, and from what I've played so far it is very obvious that every single guy has had a lot of love put into them, but I think the main problem here was the decision to limit this to only 151.
The game is designed around having only 151 so I don't really know where you would include more guys without even more scope creep, but it just feels like a lot of effort was put into the concept but the most fun part of the concept just wasn't done as well as it really could have been?
My friend is a massive Mario RPG fan, and was excited for this hack, but lost basically all interest upon finding out there were basically no Mario RPG things in it outside of Exor, who is a legendary. She also brought up that Alpharad mentioned the dev team had trouble adding Special Attackers, and that Mario RPG has a bunch of wizard and mage enemies that could have helped. We also realized that Super Paper Mario could have helped with the very noticeable lack of Psychic types, since that game is full of weird psychedelic enemies (Cursya is maybe the most obvious thing from that game to include IMO). If your favorite Mario games aren't World, the first two Paper Marios, Mario 64, or Odyssey, you'll probably be at least partly disappointed in this.
We actually got frustrated enough at the dex we started coming up with our own additions, partly because its just fun to do. The team has done a lot of work on this game already so I suspect that anything besides bug patches won't be released, but man, it really doesn't feel like the full potential was met with it. I really don't like being negative about a game I've been excited about for 3 years, and maybe that's on me for setting expectations too high, but I wouldn't have expected any of the non-Pokemon additions. Even though those additions are probably the most impressive part, they also probably ended up overshadowing the part of the game most people are going to enjoy.