Investing in just couple of Right 4*s will help you out in the long run. Shang chi and Magneto are absolute Monsters.A 4/40 Starky was my collector killer when I fought him, Took 10 revives but he did it. R5 Shangchi may fight collector better probably.Juggs is pretty good option too.Yep, iso is like that when we start. It builds over time.All the best!!
In your case mate an R4 is an R4 with highest health among all of those.But also 4* Mags is more helpful against all metal tagged champs in act5. I think the decision on you. Cuz all three have their advantages.Jugg mags first.And Shang chi has a learning curve to bring best out of him.