Thanks for the reply. I have indeed searched this thread (keyword: boss), and found a few people with the same sentiments. That it is way too difficult to beat this/they gave up.
The issue with my playthrough randomized is I cannot breed for GP due to eggs churning out random mons + the 2 fusion mons to help contribute some dmg in the fight are simply pikachus.
Thinking about it some more, I realize this game has an emphasis on the introduced elements that people are probably not used to (notably planting berries for money, GP, cards), which seem mandatory to beating the game.
Personally I think It is a design issue if the game is unbeatable without either grinding 100 hours (which is just repetitive and doesn't require any skill) or cheating. I cannot name another game mainstream or well-received fanmade singleplayer that requires this. It is not even an extra uber-boss/challenge, it is the main storyline that cannot be progressed through. It really does seem that you need a fully decked out roster of shiny/platinum and cards with max ev/iv simply to beat the game. Even games that are litearlly grindcentric like aprg such as diablo you can beat the game (the grinding is postgame content).
Really this game is very well made until this boss. The puzzles during the playthrough are harder than the mainstream pokemon games, and can definitely be hard for a child to play through.
This boss is just completely on another level. At the very least randomizer run is not balanced at all, if you search up "pokemon empyrean wt" on youtube you will find a few youtubers that simply cannot beat it, and these are youtubers that clearly have interest in fanmade games/played through multiple ones. Also comments on these videos agreeing on the absurd design of this boss. I'm sure people who are stuck at this phase aren't single digit mouth breathers but are just frustrated fans of pokemon games.