Well, i didn't consider quanta cost intentionally, that is not making it less powerful, just more costly!
Quanta cost should be set accordingly to power, therefore it shouldn't be factored into power.
The three rounds time was calculated already (that makes it 3 times more powerful than a single PU).
If it was only one round, then keeping up a duplicate (with significantly more quanta) would make it on par with the PU, except that when your copy is gone, you could switch to PU another. (Ideally, small quanta cost shouldn't be a big issue, decks usually are not on the edge, especially pure darkness decks), they can always afford 2 quanta.
So, again, this is 3 times more powerful than PU. It is only slightly mitigated by the darkness ban, 92% of the targets are still valid.
The 2 elements requirement is good (still just quanta cost though), so it is not to be factored into power. But 1 light quantum obviously worths more than 1 darkness quantum, usually. This is also not completely true, because you also have rainbow decks.
Lets take a hypothetic card cost: a quantum from every color. (that's 12). Is it more expensive than 12 quanta of one color? No.
So, for a rainbow deck, the fact that you have to pay the duplicate cost in light quanta is actually a benefit, not a setback.
In rainbow decks, this card would easily replace PU. The cost difference is 1 quantum, for a renewable PU that you can keep up on 3 creatures. Totally worths it. Even if you do it only for 3 rounds (3x2 light) still only 6, easily matched to the 6 aether cost.