I never made it past the pirates caves on "normal" before I started over on "tactician" mode, so maybe I'm not the best judge on how hard it gets in later stages... but...
From the best I can tell, the game isn't actually any harder on Tactician mode.. yeah, I have noticed a few fights with a few extra enemies, but otherwise it feels basically the same.
I "CC" the enemies and mow them down all the while wondering why I have melee in my party, since another bow user would probably be better.. 2 bows 2 casters = win.
If Fallout 4 weren't coming out tomorrow I'd be tempted to start over yet again and try a lonewolf tactician mode, as that might actually make things harder..