Black hole isn't really OVERPOWERED perse... but unbalanced definately
Useless against a mono deck, crippling to a rainbow, now maybe it could even be left alone, with its obvious advantage and weakness, but maybe theres a way to balance it a little more (take a minimum of X quanta even if theres only 1 type, and a maximum of Y quanta even if they have all types?)
Quicksand probably needs to be changed so it can't be used to deny ALL quanta at such an early point... the 1 3rd of pillars/pumpspell ideas by Kael Hate look perfect
That said, I don't see any REAL need to change any of the cards, some are rather powerful, but that's really a perk of picking the right element now isn't it?