Five Star Variants
With the introduction of 6 star champions and the massive, MASSIVE boost to atk, def, hp, there is no reason to withhold certain champions from being 5 star variants any longer. The unlocked ability or overpowered argument is moot at this point. Most times a well placed combo from a 6 star crushes all of these 4 star only characters.
Another reason why they should be allowed? Kabam you put us up against these so called too OP characters in both 5 star and 6 star versions and have us fight them in the name of being challenging. That's all fine and dandy but it just further reinforces the point, they can't be too OP if we're fighting maxed out versions of them in game WITH node buffs, global buffs, and everything else under the sun.
Dr Strange, SW, Electro, Thor, Black Widow, Wolverine, Gamora (5 star is OP but she has a 6 star version!?!?) etc. It's honestly time to stop the excuses and just add them. It's not hard, you have them in game already as enemies, just move them over to the five star pool.