It is really time spent making AI vs time spent making other things. With the a customizable skill system, you need to spend that much more time making an effective AI. That same amount of time could be spent on improving the game.
Think of it like this. If they are spending time balancing or improving AI, that implies they are not spending time designing Kokoro or any new character they feel like adding.
One of the elements I would like to see added to this game, just for lore purposes, but will affect game balance is if you are down and your opponent follows up with a move to either force you to block on wake up so they can combo or something similar, they lose popularity. Touhou spell card rules is more of a sport, so trying to beat them when they are down is seen as poor sportsmanship and should be punishable.