Sadly I don't see a great case for it in the current meta.
-Searing Tempest is a wickedly potent burn, but in many such fights your primary source of damage is Death (no dINT term).
-Acrid Stream's MDB down is nice, but only if you're not already posting 99999s.
-Reaving Wind is a great spell, but Mewing Lullaby is unresistable. 3-4 people rotating it from sub gets the job done when needed, often without any meaningful tradeoffs in party composition.
-Most other debuffs we can offer are either available from other common jobs, are not mission critical for SC/MB setups (circumventing gimmicks is generally more of a concern than damage taken by a competent tank), or get resisted outright. BLU cannot utilize immunobreaks.
-Most of our spells require standing closer to the monster than is necessary for traditional mages, which potentially means putting ourselves in AoE and/or aura range.
-If the fight involves adds that are not immediately killed, utilizing AoEs is much more difficult.
-Our better buffs are generally single target, so Diffusion's cooldown limits our options.
-BLU is not an effective primary healer for high level content. MP constraints, limited cure options, potential range issues, etc.
-Your mere presence in the alliance instantly increases the monster's HP pool. Given BLU's cooldown-dependent MB abilities, it's also extremely difficult to keep up in damage output.
Current mechanics simply don't give us a lot of flexibility against high level content. The subset of tools that actually matter in such strategies is very tightly constrained. If you have no better option then obviously you should make the best of it, but generally you should find some other way to contribute.