Gauge Management is Fun, Actually

[Myon88]

Take RDM for example. In the past, the base function of Manafication was to add 50 Mana to both the Black and White gauges.

I think it's worth noting that wasn't even the original function of manafication either. In even earlier points in the job's lifespan, it worked by doubling your mana levels across the board.

The reason it was changed was twofold, first people complained it made the opener unusually slow to ramp up (since you first needed to build up enough mana to be worth doubling), and secondly because it was a big failure point for less experienced players. You could brick your mana bar quite badly if you used it with uneven mana levels (20/40 becomes 40/80 taking a long time to fix).

So you have a skill that was originally designed in a flavourful way to match a specific job identity, then it got homogenized into a generic gain 50 gauge skill that half the jobs in the game have a carbon copy of. And eventually even that level of abstraction wasn't enough and they went about sanding off even more rough edges. Which basically sums up their approach to job design from Stormblood onward.