It would be awesome to have support jobs or hybrid jobs like past games in the franchise, but if you can’t actually use it for anything worthwhile than the quality of being support/hybrid/customization is worthless. BLU is cool, super cool, but the way it’s been implemented makes it worthless.
Once you have a level 50 BLU with all of its abilities and can customize to your hearts content, there are no worthwhile endevours to use them on. The duty finder restrictions blocks it from most worthwhile content and the level cap blocks it from the rest. A level 50 BLU no matter how skilled, learned, or geared won’t be as effective as a level 70 of anything else. This even applies to BLU focused pursuits like learning the primal abilities. What is more easily done: a group of 8 BLU get together and take on a primal to learn abilities or a BLU or group of BLU just party with a single level 70 to take those primal out faster and more efficiently? BLU isn’t even equipped to do its own activities better than a level 70.
Not that I think it has anything to do with how BLU was implemented, but as a FFXI player of four years during its hayday I’ll say, “No thank you, SE.”