Technically speaking rebels are easier to get, they have been in game longer and the requirements of the events have been known and accessible longer. Players playing a year before DR launched would have had an easier time getting a rebel squad together than a DR team, but that's just an example.
Anything referencing lore or iconic status doesnt matter and has never matter and has been stated to not be a focus of the game from the beginning.
From the conception of the game, the squad lineup has been stated to be a "sandbox" allowing you to set mortal enemies or charclacter from different eras shoulder to shoulder and fight your enemy, teams not making sense has been a thing well before them and has never had a bearing on the game, it shouldn't start now.
