I feel Ground Zero is skippable. Yes, Rad Therapy and GZ are both fantastic for procs, but Ground Zero still need accuracy, and long animation, like--wow. Rad Therapy has an high base accuracy, which means you can go with procs alone, nothing else. I took tier9 at lv49 for set mule, it's a great place to slot like Gladiator's.
Fun fact; Gamma Boost slotted with end mod IO is actually stronger than P Shifter's. It also provides End/Recovery debuff resistance.
Particle Shielding gives 50% recovery for like, 30 seconds I think? [PS on auto is fantastic--I don't use it for recovery, absorb/regen is amazing.]
Mids don't reflect everything, always test stuff ingame.
Edit: If you have a solid AoE from primary power along with Rad Therapy, you can skip Ground Zero. Otherwise, you'll be standing doing nothing for 3 seconds. It does have a buff for your teammates, but it's so ridiculously small. I took GZ on /Fire tanker, because lolCombustion.