I'd argue Black Mage is as refined as it gets. There's a certain simplicity to being a cannon, and Black Mage is a smooth and natural learning experience.

"Fire means damage, ice means recovery." <= Early levels.

"Transposing is meant as an emergency...ooooh." <= When you get Fire3/Blizz3

"Thunder enables Thundercloud, the single highest potency ability in the game..." <= Until Iaijutsu 3. Jerks.

"Positioning is key." <= Level 50 dungeons and trials

Much like every job, the progression stair leading to what we have now is readily apparent, and Black Mage wasn't changed that much with Stormblood. Black Mage is as refined as it gets. The issue is that currently the top of that stepping stone sees only very minor rewards to the rung that came before. In this regard, the 'lazy man' approach of simply tweaking numbers is an appropriate response.

I'd prefer something more interesting, but more interesting is usually what occurs at expansions so...