The average advantage from the User's entropybow against a duo might be worth 6 .
Maybe this will help. I ran some calculations for approximate average usefulness for a deck that isn't rainbow.
(2/12+8/12+2/12+2/12+1/12+1+1+1/12+2/12+1+1+2/12+2/12+1)/14 = 0.488 ~= 50% chance of a permanent being useful (not rainbow).
I used 2/12 chance of being useful for most of the ones with activation costs and pillars. I used 8/12 for Pendulum but only 1/12 for Soul Catcher. I gave Empathic Bond and others a 100% chance of being useful in any deck, though a bit less might be more accurate.
For a rainbow, I'd estimate at least 90% usefulness per permanent, which is a 66% chance of all four being useful.
That is why I suggested it generating one creature and one permanent. A creature will have a more balanced chance of being useful between the two players, while a permanent can often be dead if you're not running rainbow. To me, it just seems to currently have potentially far too much power for its cost and the fact it does not require any other cards to be powerful.
That would be more useful if you multiplied each chance by the value (CastingCost+2)
Value
2|2 Pillar
2|2 Pend
7|6 MG
8|7 UG
5|6 Nightfall/Eclipse
6|5 Cloak
5|7 Boneyard/Graveyard
2|2 Soul Catcher
5|5Catapult/Trebuchet
7|6 Emphatic Bond/Feral Bond
6|5 Sanctuary
6|6 Golden Hourglass/Electrum Hourglass
2|2 Sundial
5|4 Flooding/Inundation
Chance of useful [duo] (I assume the 90% usefulness value is accurate for rainbow)
[11/121=1/12] Elemental Pillar/Permanent with an activation cost/Soul Catcher
[11/121/2+1/2=7/12] Pendulum
[1/2] Quantum Pillar
[1] Permanent without an additional cost
[1/121+22/121/2=1/11] Nightfall/Eclipse
My result assuming that all pillars total have 1/14 chance (1/14/13 chance each) is that the expected value per permanent is 2|2 for duo and 4|4 for a rainbow.
Net gain per permanent each is 2 quanta value. (assuming a rainbow vs a duo)
4 permanents each should cost 6
|5
+1 draw = 8 quanta value.