Originally Posted by IvanLedah21

Stats and possibly passives. But ultimately, the passives are more or less useful depending on what other units you have. Rainbows are OP in general, but for maximum benefit you'd want skill synergy. Also, if you use auto-run + afk, then units like Dogwood lose a ton of value because their passives focus on Solar Blast.

Very true, I've used some squads from the bottom of the helper list which featured 4-5 lvl 70 rainbows, but weren't really notable in performance.

As a simple (and should be pretty obvious) example, Fritillaria by herserf can barely hold a candle to Black Baccara as a rainbow. However, in a squad with a couple of Activation Rate boosters she really takes off. Doesn't really matter if those boosters are rainbow or gold, but she's performs more like a weak gold card when put in the wrong squad.