Ive Fifty-one 7-star toons. Add some sub-7star notables, like Baze, Nihilus, Thrawn, Sith Assassin.
12 of my toons are at gear XI.
I do not recall when was the last time I could not complete my daily-ish GW.
I rarely get a broken node 12, apparently, my squads never topped whatever formula is there.
Lately, I get some of these AWESOME Thrawn based squads in node 12. Hard!
I have to think it and often restart it for the win, and it usually takes me two squads. I enjoy the challenge.
I use about 7 different squads. Not only is "insurance" (I have 7 rosters of primed, mean squads, in case of a tougher node 12). This is also a "get to know your toons" strategy. I play with my TM squad, R1s, Jedi squad a couple of rebels, my of Sith/Empire, other non-synergistic but tough squads.
I use them from lowest to highest, but even my lowest can handle well the lowest node (sometimes w/o a scratch). Try it when you get your deep roster.