Basically title. If banes survive rolling through a storm with one health because of their regeneration, why not buff storms damage by 1 per tick? As far as I'm aware that wouldn't heavily impact any other interaction. Even if it did, however, with the current state of toss that might not be a terrible thing.

Another idea is giving colossi an upgrade that would allow their attacks to leave fire on the ground like in co-op. This probably wouldn't affect Pvt as much because the Terran army is moving and splitting and it's already pretty impossible to engage a large colossi count without loads of Vikings to snipe them off. A zerg army that would have to move through the fire, however, could take a loooad of extra damage. It could give protoss some zone control in pvz and midgame power which it desperately needs.

Also a potential upgrade to increase stalker attack speed so they're better at fighting lings. They still wouldn't be good vs lings and banes, as they shouldn't be, but a small increase to make them not useless in the situation might be neat. This change should again affect pvz more as EMP and marauders should pretty much always keep stalkers in check and it being an upgrade should keep it from powering up blink allins too much.

Just some ideas to help protoss in the matchup, the first suggestion is by far the main one though so let me know what you think and whether that one damage buff would break any other interaction irreparably.