I would miss it if this wasn't a multiplayer game.
Build variety is something single-player games excel at because the only consequences for a good or bad build are an easier or harder time clearing content. Your build only affects yourself and consequently, you are free to do ANY build (And in case of doubt, you can go into the options to tune down the difficulty). You can even make builds that are purposely gimping you and then tie achievements to beating the game with them as a challenge! Alternately, you can do Failure fusion a couple times and one-shot everything with an OP weapon while laughing maniacally. Completely broken in an MMO, but in a single-player game, it works and is great! In general, I think many RPG concepts simply work better in single-player games - lasting consequences, permadeath of NPCs, razing or shutting down locations etc.
In a multiplayer game, if you purposely gimp yourself, don't expect to find groups, achievement or not. Your actual build variety gets massively reduced by the demand for group performance. As such, I don't really mind not having much to pick at all and am fine just having the different builds (jobs) delivered and balanced as a complete package. It makes it easier for me, too, since I don't need to do as much research. And in the case of FFXIV in particular...I do like not having to level ALL jobs on all my alts AGAIN just because one might have a crucial skill I need. The current cross-class is already quite annoying and I'm somewhat looking forward to having it replaced with the role based system, because by now I've leveled lancer to 34 a total of 4 times and I never liked the class to begin with.