As much as I don't mind people playing WHM, this is a pretty poor comparison. Fighting games are competitive 1v1 games - by picking a character that isn't strong you're only potentially hurting yourself. In XIV (and MMOs in general) by picking a job that isn't strong you are affecting 7 other people's chance of killing the boss.
Eh, not all of them. The example I actually had in mind when I wrote that was Smash Bros., which definitely isn't always 1v1 and is infamous for being picked apart and having its characters placed in "tiers"

If there is content that a class literally cannot complete, I'm sure it will be taken note of and corrected. In the meantime, player ability is going to account for way the hell more regarding whether or not a raid can be completed.