Combo moves are meant to be strong at the cost of being a pain to pull off. Also, due to how the game engine handles things, making combo skills work that way would be even more annoying than the current version since it'd have to check if the character is alive, if they're in the party at all due to certain fights removing characters, if they have enough Mp, if they have status effects to see if they have the appropriate amount of Mp... and as you can see from certain skills like "Dispel All"s, the engine doesn't like when I tack on a lot of conditionals anyway.
Again, due to certain fights where party members are removed/restricted, I have to add them all back in through the engine's Common Event system, so it all gets reordered the same way every time. While I could let people order their own way, I can't store the info on how you reorder them, so I felt it'd be best to prevent that and have frustration over regularly having the locations reset, and instead have the consistency.
I did have more character interactions and skills/combos I wanted to add in, but making a thing like this takes a lot of stamina, and I eventually had to cut things back if I was ever going to release something I could call "complete". I'm not done with the universe/characters and I'm making a new game with them (more combat systems focused, like a boss rush/puzzle game), but I really don't have it in me to work on this game outside of bug fixes. It took two years and the game engine was screaming all the while. There's a reason people don't make things quite like this in RPG Maker; it absolutely hates animating and keeping track of this much stuff, and the workarounds I did to make it at least this playable are many.
It doesn't want me to add anything more, and I'm fine with that. I'll make other games with some relation, and maybe I'll write up some short stories of interactions I couldn't find a good cutscene place for in the game and add it as a word file at some point, but I have to move on from this game.