Disagree. You can't cap cold (or psi) resists, and you'd be hard pressed to cap fire or neg. While I'm sure you could soft cap S/L and melee defense, it's certainly not easy and not sure how you could without gimping your offense. It also has no DDR, so your defense can get stripped away easily. I do like Rad (my Rad/Rad scrapper is vet level 45 or so) but I don't rank it at the same level as Invul. I find Rad is more of a hybrid resist/regen set, but sturdier than Willpower.