I don't remotely consider this a backdoor approach to talents. I don't like talents. I just one stat that I've been willing to test at every amount possible under i390 despite some throughput loss as having genuine gameplay appeal and find it more than a little disappointing that it's only permitted to two jobs.
This seems like a contradiction to me. What you want, effectively, is to have an alternate gameplay dynamic available to each job (in this case, faster GCDs in particular, but I presume you wouldn't hate other gameplay-impactful options). If that is the goal, then a talent-like system is the better way to achieve it. It's direct, it's clear, and it's flexible from a design and balancing perspective.

I'm actually not very familiar with other games' models, but one could imagine something as simple as selectable traits a la PvP (but more impactful). The number of slots could be flat, it could be something you gain over the course of the endgame, it could be on gear, whatever. Or it could be trees, or sets of talents, or some other model. And balancing such traits need not be all that difficult, depending on how they're designed. It's really a wide open space, there's no reason at all to limit one's thinking to the way talents have been done in this game or that game in the past.