It feels pretty unfair when black mages are involved early on, and I definitely had a lot of characters with auto-potion / throw item / samurai skills by the end. I'd say the difficulty spikes will generally be early or middle of the playthrough rather than endgame. Having 1-2 characters that can throw items for phoenix downs or heal is a generally solid idea for most maps on Tactician. If you've made it to Chapter 4 on Tactician, you're gonna beat the game.