Honestly I think BLU has been brilliant.
Sure it had a bit of a pitiful start at just level 50 and it would be nicer if it could access some more content, but I've had groups of people playing just BLU to learn skills and gain achievements for the Morbol Mount.
It's kinda like there's three main facets of content right now that I can engage with other people in: Raiding (savage or extremes), Relics (Bozja, DR, etc.) and BLU (Coils and Alex savage).
Notice that means the other 17 jobs are bundled together in everything else, but BLU stands out on it's own. 'Limited' really is a misnomer, it makes up for it in other ways, other strengths, that other jobs can't fulfil.

BST could do something equally as impressive if it built upon and expanded the companion system.