Personally I think Quantum Pillar is Overused, not necessarily over or under powered.
Zanz made query about its overuse and as part of his balancing was looking at weakening it to fix the overuse. This worked with Steal and some of the other cards but I think it would fail here. Removing its unlimited status and adding a range of other multitype quanta generators would divide its count in the statistics probably evenly among Quantum pillar and the the generators of the same strength.
It is very hard to define when pillars are overused. Rainbow is a term for a type of deck, which holds HUGE amount of DIFFERENT decks.
If you can make 5 viable decks with pillar X, and 1 viable deck with pillar Y, first thing you can conclude is that is not a pillar problem, but problem of cards that relate to that pillars. Second thing you can conclude is that it is perfectly normal for pillar X to be 5 times more used than pillar Y.
And if we decide that rainbows are overused (thus increasing the usage of its pillars, and all cards that such decks usually use), than we should seek the problem in other types of decks, not rainbow. And problems do exist with other types of decks - lack of cards to make a rounded deck.
Adding new/different quanta generators *may* lower the usage of pillars, but that wont solve any real problem. Rainbows will still be used, the only thing is that instead of pillars, you will have a cards named hdkfiowp and sudbgkrh.