Not sure if this relates to the problem of buttons, but the choice to homogenize the jobs is sort of a design decision more than a right or wrong thing. As I recall, one of the things that Yoshi P. had said ages ago is that he would not have locked jobs behind using specific weapons, as it would make sense a warrior might use a sword, axe, hammer, etc, and wizards would probably use wands, staves, books, whatever they need as a focus. Homogenizing the jobs is a compromise where you technically are playing a different job, but the skills under the job are linked to a role rather than a class, so that way it is more an aesthetic choice which one someone plays. Sort of like having a prebuilt specialization in other MMOs.

Its also a solution to getting people out of a ditch they dig for themselves. What I mean by this is that if the jobs remained unique completely, one advantage would be each job would be an experience onto itself, and if someone wanted to play that job to the highest level, they'd need a good chunk of time to get used to all the skills and how to use them right. This in turn can make it intimidating to swap to another job even in the same role since the two would be completely different even if they share the same gear. So having them work more closely like each other means that it is easier to try different jobs.

The part that is sort of hidden under all this is that homogenizing the jobs is also a way to make it easier for developers to support the jobs. They keep wanting to add new jobs each expansion, and if they kept the original jobs as complex as they were, each job would require unique maintenance from the developers to make sure it was still playable. So this is them trying to modularize jobs so they are an aesthetic choice in a role and role skills are what the base skills are of the true class.

Just throwing this out there since someone earlier was starting to talk about the job homogenization and maybe was thinking this was simplifying the skills or making the skills more complex when it's kind of its own thing.