Heya, I've just recently finished the game and figured I'd leave some feedback for it, cause it was an enjoyable experience and I figured I could share my thoughts on how to improve it more! Feel free to point out anything I might've gotten wrong, since the game is new, I couldn't find any info on it whatsoever besides what you shared here.
Overall difficulty
-I think the game was fairly balanced in terms of the difficulty. I tend to be someone that looks for challenge in fangames, but as you put it, this was closer to the mainline games. I will say the final few battles did seem harder, but it's completely within reason. Imo you handled that well
-The level cap seems... a bit lenient? I've never hit it even once, so I'm actually unsure of how it even works. I'd presume it to be based on the average level of the next bossfight, but it might be the highest level mon they have? Don't hesitate to be more restrictive with the level cap, as it's an optional tool for people that actually want it to affect their experience.
-The balancing itself seems quite good. Ice is a bit stronger, and fairy a bit weaker. I will say though that maybe Prankster Umbreon is a tad too strong, having used one for my entire run (without items or EVs, and also with the level cap). At the same time it was also incredibly fun to use, so perhaps balancing may not be the key idea for them. However, the Frostbite ability is very awkward. It procs on contact moves, which are almost all physical attacks, making the status effect a bit of a waste considering it's for special attackers. Frostbite is a neat idea, but it may need a rework as it feels awkward in terms of payoff atm. Maybe it could be akin to poison touch instead?
New variants
-While some variants are better than others (my poor Gallade), I believe you did really well in terms of making them all enticing to use! It's been hard to know what to pick for a team, ahah
-The designs for them are all really cool as well, definitely something that I can say is a strong point for the game. Perhaps a bit too many fire types variants, though it might just be my imagination
-I'm unsure where to put this, so I'll just put it here, but I was unable to ever evolve Sinistea, having been unable to find a cup, and it not evolving via levelup. Seems like a shame for a Pokemon variant that's teased a fair bit by npcs. This might've been on me for never finding the item for it?
Quality of life
-In echo of what others have already said, HM moves are still an incredible pain to use. This essentially requires you to carry a flying type with you, a Pokemon that can surf, etc, etc. Even if the moves were to be even stronger the issue would remain of being forced to use other pokemon than what you may want. In addition, I'm uncertain why you have added in the inability to learn over HM moves, forcing you to see an NPC to remove it beforehand. I can imagine it could be to avoid softlocks, but that's also why we have multiple savefiles. An additional "teleport to last pokemon center if stuck" option could also work in the options menu.
-Again in echo of others, there is an issue of there being a lot of dialogue before most boss battles, leading to resets being extremely lenghty. You had suggested making the rematch a lot faster, though I believe that, from experience, people will usually reset instead of accepting defeat, as it means they don't need to walk all the way back. I have a few suggestions on how to solve this, though feel free to ignore them :
--> Giving the player a "retry" and "return to the center" option when they black out, allowing them to immediately enter back into the fight if they so choose, still with the money penalty.
--> Making the bosses do their whole speech, but then waiting on the player to make the first move towards them, giving them the time to save before doing that step and initiating the battle
--> Giving a "skip" button. I'd usually not recommend that though, as it can lead to players ignoring all the story
-Something I've not seen discussed yet is the surprising lack of healing mid-route. There are quite a lot of places where I'd need to constantly go back and forth between the route and the town to heal back my team, all the while using repels to avoid constant interruptions. This is especially noticeable with bossfights, where they happen on the middle of the route, and you are neither healed before nor after the bossfight, which just feels frustrating. Victory Road notwithstanding, since that is the point of this place.
Story
-I kinda liked the story, and the general idea with it! I thought it was a nice take, and a good use of the Aether Foundation, alongside these light type Pokemon being tied to possibly the most dangerous Pokemon out there. The main thing I'd say could be improved is the subtlety and hints during the adventure. It feels a little too little at times, and overly blunt at others. Some NPCs could talk about the lore, perhaps there would be an old map somewhere, some line of dialogue about light-types, etc.
-The characters themselves were all pretty nice. The Beastmen team might've needed a little more info on them, but that's kind of it for that!
Apologies for having written a lot, but I wanted to give detailed feedback, in the hope of contributing at least something to this game that you've made. It's been a pleasure to go through it!