This is not how I interpreted what they said in Guardians 2. Peter Quill didn't actually lose anything in and of himself. He's still the same person with the same genetics and part-Celestial heritage as before. What changed is that Ego wasn't around anymore, and thus no more reserve of cosmic energy from Ego that Peter could contest for control. Basically, he's a pyrokinetic who can't make fire, and who now doesn't have a fire around either. Only replace "fire" with "cosmic energy that is much, much, much harder to find or create". Implications for Gauntlet usage? IMO, not much. We already have precedent from Guardians 1 that Peter's weird heritage provides *some* advantage when handling an Infinity Stone, but only to a certain degree. Given that wielding the Power Stone via the Gauntlet was casual and effortless for Thanos, while doing the Snap inflicted severe injury? I think its safe to say that the Snap is orders of magnitude more injurious, which means even with Peter's genetic advantage, he's probably in the same situation as Tony Stark- he can do it and still be alive afterwards, but only briefly and with mortal injuries. You need to be at least Hulk-tough to use it and still be functional afterwards.