My first playthrough was on Balanced, my second on Tactician, I am on my third playthrough again on Tactician. From my experience there needs to be another difficulty level because Tactician does not present a significant increase in the difficulty level from Balanced.

Having completed my first game I wanted to up the challenge but I found that Tactician was no more challenging than my first playthrough. There were very few fights that now challenged me. Most were no more difficult to the experienced me quite a few were easier.

Anyone who has completed BG3 on Balanced will not be challenged by Tactician. Tactician is simply not a challenge for an experienced player.