As mentioned, I also had my hard time against Chaze teams
https://forums.galaxy-of-heroes.starwars.ea.com/discussion/comment/935380/#Comment_935380
However I was sometimes able to jump over them in the arena. Or someone else killed them, and then again I was able to take the place. Otherwise I think sometimes you have to live with the payers get an advantage for some time...
About RG, as Doitsuyama mentioned, tanks are also already viable with lower stars, only they need gear.
I just upgraded STH from g9 to g10, and just hitting the "upgrade" button pushed him from 18'500 protection (7'700 from mods) to 26'200 protection (11'000 from mods). Double tank is definately a good thing. But maybe you can wait until Sun Fac is activated? Should be farmable now. I really love him, he is so good against these pretaunting teams (often I face ShT + RG, sometimes Chaze).