Have you given a try to elder difficulty?
I'm a rank 2 valiant (bassed in 30 champs prestige) nada I decided to give a try to elder difficulty and I was amazed when found is more easy than I thought, regular figths last 1.5 minutes or less even with 7* rank 1, I have explored the the mutant and science quests and inky spent one revive but due to an error, maybe you should give a try and don't just said what someone in YouTube said, what is unfair is the lack of energy refiles.