Ah right, now I see what you mean. I guess english isn't your native language since you misinterpreted me. I didn't say that charm needs or should use rainbows. I said that out of the three classes, rainbow items shows most of its value to charm. I also said that rainbows give marginally better result when matches go over 6 blows(6 blows is the threshhold in where defense becomes better than ego), not that rainbows is absolute bonkers for charm players. And yes, I am charm. I use three rainbow items, 1 legendary single stat and 2 epic single stat and it works to my playstyle. Between rainbow and single stat epic the difference is attack versus harmony, yielding (at my level, per rainbow) 250 damage versus roughly one tenth of crit total (10% total crit difference, 5 more for me, 5 less for opp). With one crit resulting in 4000 defense for me and one less crit from opp resulting in 4000/8000/6000 less value ( on average 6k) one of every three games holds 10k different value due from crit. During three games with 7 blows the extra attack deals 5250, meaning on average harmony slightly outperforms single stat during longer battles. Slightly. Not even close to the disparity in costs. Probably not even a factor, since battles aren't exactly close or needs to be calculated down to the decimal to determine who wins.
And then again, it's different maths for HC and KH. HC definitely only favours single stat.