While I'm not going to comment on the difficulty of the game, I totally agree about your comment on the inconsistency of the displayed "percent chance to hit" and the chance to hit in practice.
During my past tactician run, even with advantage and a displayed 80% chance to hit, I would consistently miss, sometimes even two times in a row. I'm not sure whether that is due to the nature of the difficulty possibly adjusting dice rolls or just pure unluckiness. Since I have powerful team compositions in tactician, I don't need to save scum when I miss, but it's still jarring how much I do miss considering there is such a high chance to hit. Please do note that I play with karmic dice off, which certainly aids in the totally incoherent nature of the dice rolls. That being said, I do wish the percentage would at least feel accurate.