Very good points. I probably need to give the later boards more interesting shapes in order to weaken stone-spamming strategies (both yours and the opponent's) while improving strategies like fire and ice.
Regarding the uselessness of large stones like 83: The intent was that most players will not figure out the 77 combo, but will get -1 stone, so they might use -83 in their deck. And 89 is intentionally hard to use because they can potentially lead to very boring games.
Glad you enjoyed the 0 puzzle!