Well, the main issue is that the devs in XI never wrapped their brains around the idea of a hard division between RDM's potential roles. That, along with the fact that gear and subjob were supposed to help the RDM choose their role went out the window once gear swaps became the norm (because, surprise surprise, the hybrid jobs would benefit from gear swaps way more than any other job).
That being said, enfeebling is a tertiary class aspect, and as such should NEVER be the raison d'etre of any job. You can tack enfeebling as part of the job and so on, which has been known to work.
On the topic of generalists, you either have to drop/minimize the generalist part of it or implement hard divisions. Hard divisions are not possible because of the armoury system, and as such the only obvious alternative would be dropping the generalist aspect entirely or minimizing the generalist so that RDM has a focus (which compliments the armoury system) while still have a couple of extra things as is par the course with the job. Here and on the Design thread, the focus has been making RDM a magic fencer that happens to have a couple of extra spells up its sleeves when called for. It's less about the spell library being exact copies of what WHM and BLM would get, and more on RDM's unique application of magic in a way that befits a magic swordsman while still technically "borrowing" from other jobs.