I'm not sure if you're disagreeing with me or agreeing haha, sorry XD. Are you quoting that line because you're like "yeah, we should be getting a healer and tank otherwise people will be upset" (which is really me agreeing with you first lol) or were you under the interpretation that I said something counter to that?
Just in case I meant by that line if we had no info/leaks/trailers to go off or if for some thal knows why reason I had personally made the plan for SE - I'd of course follow the SB+ needs to be tank and healer, by making dancer healer and tank blue mage (aka if I could go back in time and wipe away the gunblade tank hype, which I would NOT do now - just leads to further upset). While unchained (non-DF version of blue) would be very strong/unbalanced damage/solo power with some hints to tanking style, in attempt to give DD players a palate cleanser of destruction as well as an easy and comfortable taste of tank (like SMN does, somewhat, for SCH - DD to healer, blue mage is the gateway of DD to tank). In that way while yes technically DD received no job in the expansion yet they would have something down their alley (for cleaning up old content that no one is running, also where normally wipe mechanics can't be solo'd, and getting a wonder of what it'd be like to be tank, maybe converting some people along the way). Of course if they go the three job route then everyone gets one job, given enough time (Tank/Healer right away and DD a bit later via advanced blue).
As for the idea of spells = gear/ilvl, that's an interesting concept.. Obviously it'd need a few systems, checks and balances, but given enough creativity and careful crafting it might work~ Certainly would be a different concept. Worse case scenario for "gating" some of the progress like other jobs have with weekly tomestones would be unlocking special arenas to learn spells from (you unlock fights against special monsters that have spells to learn to up your "ilvl", or less fun increase the % of earning a spell that's hard to get).