I agree with you. The game should not be balanced around very specific skills like thievery, however:

You definitely don't need to do stuff like that to get through Tactician mode.

Me and a friend play. 2 chars each. We are in Act4 now, so I can't speak for end game.
So far we have stolen one item, just to see how it works.
We make our build up as we go, none of us have read up on skills, builds, story or anything. We have never waited to refresh shops (not that it would be a point, we can't afford much)
We just started the game and play.
Some fights are hard. We have struggled with a few, but most we just came back to later after gaining a level.
It should be hard, as it is currently the highest difficulty in the game, so it's good that we have to try more than once on fights :P
If we had restarted now, with our knowledge of builds and tactics, we'd have a breeze, I am sure.

You don't have to abuse anything, at least not in the first 4 acts

As a final comment, I'd like to point out that calling people who use the games different mechanics "EXPLOITERS" in caps no less, is not constructive. If you think that stealing is too strong, then point that out instead.