Still on Act 1 with Tactician but whilst it's harder, it's more in a "You have to blow significantly more resources per fight" way than a "You need much better tactics" kind of way so far. I mean, you do need better tactics, but like, the tactics that would make a fight easy as hell in Normal make a fight perfectly doable in Tactician, just you probably need to use more long-rest resources to pull them off.
Long rests cost double but given how much food you find that seems unlikely to be an issue. Of course it's possible some really high-end fights in Act 2 and beyond will be much harder.
Weirdly Larian said that they'd given enemies loads more things like bombs and special arrows in Tactician, and put more dangerous things around like exploding barrels, and like, half-way through Act 1 I've seen no evidence of either - just a LOT more HP on the enemies and generally they seem to be a little higher level.