Usage doesn't mean a card is OP.
For instance, there are cards that I use because they are fun.
I consider using a rainbow deck to be more fun. I use a rainbow stall, because I enjoy rainbow more than mono, and stall more than rush.
However, I tend to lose, because my deck is full of cards that I think have interesting abilities.
Also, if a deck needs more quantum towers to generate quanta than a mono deck would need elemental towers, that would be a case where usage would actually mean it was UP.
Show me conclusive proof that quantum pillar/tower is OP, other than that people use it, and I may believe you.
Furthermore, by your logic, Fire Pillar is definitely OP, when you compare it to other pillars.
And, many cards are way more OP than Fractal of Graboid.
In fact, every pillar is way more OP than Graboid.
Point is, don't be hating on quantum tower.