You have way more freedom as a class; some of the action restrictions with jobs can be detrimental in places. I'm sure ARC is better DD than a BRD (because ARC has access to Blood for Blood and can potentially build TP faster with Invigorate). PGL is better defensively than MNK from what I've seen (PGL has Second Wind, Cure, Bloodbath etc, MNK is restricted to Second Wind).

Classes are extremely versatile whereas jobs have their own place too (BRD is very handy for DD and support; while its DD capabilities aren't as good as ARC the ability to use songs to benefit the party is a nice boost).

You're just seeing everyone use jobs at the moment because they're new and everyone is trying them out, getting AF gear and so on. Give it a couple of months and I think you'll see a bit more diversity (more jobs than classes, but some people will ultimately go back to the flexibility of classes).

So no, I'd rather keep both. Retainers have a moderate amount of space anyway, I've never really needed more than 2.