You have to incorporate the rng factor. Don't start a game thinking you'll do one strategy, work with what you're given.
Few games ago i played someone who'd got the brawny units get 50hp per kill item. Didn't think it was much good myself, but he managed to get 3x 3* brawny characters and they soaked up so much damage it's unreal. I even had an enigma 2* that does %of life damage as the alt and i couldn't kill them all before losing.
I'd probably never have run that build before, now I'm desperately hoping to get it
.