If you have to resort to pools and incarnates to be survivable, you're playing it wrong. Having perma Particle Shielding is much more useful. You don't mention that it has a big hole to cold damage, which can be an issue fighting BP in end game. I like Rad Armor, but no way is it sturdier than Dark or Electric.
Does fine against straight up damage, but folds like a wet noodle when hit with -defense or -regen. I would place it in the C tier.
Placing SR in the C tier is absurd. Its definitely sturdier than Willpower or Fire. Not many layers? How about the scaling damage resists that can cap resistance to all damage types. Really doesn't need +absorb or +regen.
You do know you can slot other defense sets than LOTG? My SR has none, nor does it have Ageless, Support, Superior Conditioning or Physical Perfection.