Ok but why does that have to be mutually exclusive to these classes being playable in the rest of the game (mostly venting, not saying you yourself said that)? You already need to get specific skills for BLU to get through job quests, so it's not like they can't combine the learning experience and progression. And Mind Blast and Glower were made 100% obtainable on enemy kill, exactly because they were blocking job progression.
They literally have in place a system that would enable BLU (and subsequent Limited Jobs) to be DF ready, and have already made adjustments to skill acquisition towards a similar end. They can do all that, without taking anything away from the content exclusive to the Limited Jobs.
By all means, introduce classes with their exclusive content. They did it before with BRD. But on release they disproved a lot of things they said about BLU, and since have only taken steps to make BLU even more DF friendly - now it's a matter of will rather than ability.
tl;dr jobs having interesting, unique side content is not mutually exclusive with them being DF friendly and we shouldn't be fighting each other over it, but the devs.