I've really only ever seen BLU as side content with a new way to experience the game and try some battle puzzles. I think it works very well like that and personally hope they add Beastmaster as another. I feel the variety adds to the broader experience of the game as a whole.

My only real issues revolve around it not seeming to be sure if it wants to be a solo experience or not. While the endgame is mostly the The Masked Carnivale, a single player experience, some vital spells are locked in dungeons and instances too difficult or tedious to reasonably handle solo. And the leveling process itself feels very archaic, practically demanding to be power leveled past 40.

Personally, I think they should just lean into the solo aspect. Make it extremely easy to level up, but not over 10 levels behind your max job. Adjust the learn rate for solo play so you're not begging for a party or replaying the same fight 20+ times.