With the relase cards like Raven who does his job but aren't as vurnable to SoA and has higher power (7 power is weak for 5 star in current meta), kolos shouldn't be banned. He can't 0HKO anymore. He has 5 stars. Nightmare isn't really strong clan in general so it wouldn't be OP for them. Just my 2 cents.
I had 1350 elo in a past, im not a random kolos lover, also i don't play Nightmare, i just think this clan is cool and deserves some love and this elo ban is not fair in my opinion.
I was able to use rhatana once in ELO.... once, and i'm telling you she should just stay where she is now, together with Lou, as much as i love Roots those two are just too amazing to be re-released.
The amount of non bonus-SOA cards are quite low and most of them have low damage or are bonus dependent to function properly. Also, Nightmare kinda has a full line of scary abilities, so if you play your single SOA for a bluff Kolos that does not guarantee your win . Fear factor is the to this game, it always has been and people who can capitalize in this are in this weeks top 20 list of ELO players.