Balance, Accessibility, Diversity

[Satarn]

game starts off with a unique and diverse class lineup
game introduces raiding
raiders complain when specific classes are more useful than others
developers start removing the uniqueness from classes to satisfy raiders
raiders complain more
rinse and repeat.

Your obvious raiders-hate-boner aside, this doesn't even make sense when you look at the history of the game.

FFXIV had raiding pretty much from the very beginning in ARR(1.x doesn't count). I think most people will agree that jobs were at their most diverse back in Heavensward - when raiding was very much there and at its most hardcore to boot. The HW era had something else to it though, specifically in the jobs department - they weren't just diverse, they were also very complex and therefore not all that casual-friendly.

The homogenization of jobs wasn't for balance - it was for accessibility. The more casual part of the playerbase complained about things being too hard, too "clunky" as people often say and in order to appease them, SE started dumbing things down, simplifying and cutting out each job's unique mechanics and as side effect making them less diverse. Then those complaints continued in Stormblood and 5.0 dumbed things down even further.
Those "raid focused" games you speak of - were they not also more and more casual-friendly as the time went by?

Interestingly Eureka - which is as far away from the raid-style content as XIV ever got - came in 4.x and somehow the expansion after adding this new, "refreshing", original, non-raid content, things are getting less and less diverse. We are going to get more Eureka-style content in next patch series and somehow SE didn't give us more unique options in preparation for that, how come? By your logic, Shadowbringers should be when the jobs are at their most-diverse, but alas here we are.

I've said it many times and I'll say it again: balance(and by extension raiders) are concerned with numerical outcomes, which can be equally achieved with as diverse rotations and job mechanics as you could wish for.
Balance and raids are not the issue - that is unless you're really hell-bent on playing a job that's solely focused on non-combat utility like Peloton or decreasing people's fall damage, in which case you should probably look for a different game.