Aight, so reading through this and I can't help but think that there is one key point being ignored or just isn't considered
The "canon" way to play Rejuv is on Normal mode. If you want an easier time or you want a bit more of a challenge then you have Casual and Intense mode, respectively. Or to put it simply, casual and intense mode are extra features. I think it's a bit unfair to expect the devs to develop this game around the needs of Intense (or Casual) mode. Sure, QoL are always nice and I believe they are steadily added into Rejuv as more are thought up and suggested (obviously, not all suggestions are taken into account. Some are too low priority or a bit unreasonable). But at the end of the day, the main focus of dev isn't looking at things from the perspective of "how is intense".
Now, just playing JRPGs in general, I'm personally not a fan of grinding to reach a specific end result (i.e. getting a specific character to specific level with specific attacks/abilities). So I can definitely empathize with what you're saying. But from what I'm understanding: a lot of the critique in your post looks like "intense mode should allow access to a formalized version of pokemon editing to save from the mindless grind". And I think the easiest solution to that is: just turn on debug and use that. It's a one line change to enable/disable it and should allow you to breeze through any of the mindless grinding.
I can't guarantee what future releases may add into the game. But to expect that specific features would be added for a certain mode only might be expecting too much as, once again, the game is developed and planned around Normal mode