I see so many garbage BLUs, it really saddens me because I love the job and I think it's really powerful and versatile. The garbage BLUs are the ones that only wanna do physical attack spells and solo skillchains. These are important things for BLU but if that's all you wanna do then you fail.
Nyzul Isle for example is something a good BLU can really be useful, I used to go BLU to Nyzul before I leveled SAM and people used to say "wow didn't know BLU could be so good for this" and I was kind of surprised because I thought all BLUs did what I did. As I started to go SAM I got a chance to do Nyzul with other BLUs and I was truly shocked to see how crappy a garbage BLU could be.
I once had a BLU in my group and the floor was specified enemies : Chariots and this BLU didn't head butt a single aoe, he instead used disseverment a lot and gave the chariot massive TP enabling it to do even more aoes, obviously we wiped, our RDM couldn't cure fast enough. Versus chariots a good BLU with Homam can easily head butt every aoe the chariot throws if he/she focuses on that task, making the floor extremely easy.
Just the other night I was with the worst BLU ever, this guy didn't even have Magic Fruit set at all. BLU is so good as a backup cure, it can really save the day in this way. Solo or in pt I can't imagine not setting Magic Fruit. Also this guy didn't set Diamondhide (When I go BLU to nyzul Diamondhide was a huge lifesaver, I'd cast it once at the start of every floor and before and during boss fight to absorb aoe dmg, it really saved the RDM a lot of MP and hate). Also before we engaged the boss I specifically said I would 2 hour as SAM (since I'd gotten a revitalizer) at the start as to not be interrupted and of course as soon as I start my 3-way Light solo sc this crap BLU self-scs and fooks up my sc.
I know I'm taru and I have close to 900MP so i can afford to be more versatile, but if all you do is cast physical attack spells as BLU (other than when zerging) then you're not doing it right. BLU is such an amazing job to waste, it's a DD, a zerger, a healer, a nuker, a buffer, a stunner, an enfeebler and a sleeper all in one.