Considering their armory system was one of their main selling points I really don't see the design decisions of this.
This doesn't in any way interfere with the armory system. None of the locked-out gear is necessary for your jobs to be playable. There is enough gear accessible outside of locked content to enjoy pretty much everything in the game. You will probably need more for turn 5 but that's about it, and even then you don't really have to have all lvl90, so you can spread that stuff out across a few jobs instead of stacking it all on one if you are concerned with flexibility. While making alts is an option for the crazily-dedicated it truly isn't necessary as much as people are acting like it is.