The only skills on BLU that look like they'd have the potential to be busted in standard content are:
Instakills/HP reduction effects (Which wouldn't work on trials or raids due to ?? bosses being vaguely considered higher level then you),
White Wind (This could allow for ridiculous amounts of pinch healing if the healers just toss the BLU a few OGCDs after an AoE).
Bad Breath (Assuming the damage debuff works on everything)
Eerie Light (It's basically a way better version of Garuda-egi's magic vulnerability debuff).
Everything else has fairly reasonable effects and I don't think the insane potency on Self-destruct/Final Sting would ever be worth a weakness debuff unless it's at the very end of an encounter.