I'm sorry that it took me a long time to reply. But I appreciate the feedback,
@LeavingUndad The katana/nodachi being fairly rare as a loot was intentional, from my part. But I'm pretty sure I never altered the quest rewards as those should still gives you bokken/katana accordingly.
Bokken/katana rarity in merchant depends if there are other mods that adds item to the same merchant. More items=less chance of bokken/katana appearing. If fep+ merchant still didn't sell proper weapons according to your level, then I could probably do some changes to make bokken to appear more common. Also I check that bokken can goes up to level 25, that can be addressed as well.
Kensei's crash was related to Fine Control's passive and should have been addressed iirc.
I'm glad that Mongol Archer can be played without having to worry about crash when assigning stat.
The fix was all thanks to
@Epoch and I can't thank him/her enough for that