You can’t afford to give Zealots and Stalkers stat buffs because proxy 4 gate would still be a valid build w/ or w/o warp gate. Slow-lots with stat buffs being produced out of 4 gates when rax/pool are barely finished would be impossible to hold.
I think the solution would be to add more upgrades for Gateway/Robo units to compensate and at least provide a delay for proxy shenanigans. I’m not sure what they should be though.
In addition, Protoss still has recall so they’re still more than capable of removing the issue with being out of position. Though, the correct solution would be to not take their entire army across the map every time; they’d have to start leaving behind defending squads (like Zerg and Terran have to)