Look, I get that you are a Terran player and don’t know too much of PvZ, you said it yourself, but try tô understand how dangerous the Mutalisk are to the Protoss.
The response to unscouted Spire is to wait for 3 or more Phoenixes after trying your best to defend with forced Stalkers warp ins and try to macro the game behind, and you will be behind because you can’t move out with 20 workers behind and try your luck in the late game.
Or you just try to warp in the best army you can with Stalkers and basetrade all in fast because every second you are not all inning the Zerg gets stronger, Zerg just have to wait until the Protoss step into creep and get swarmed by lings. Stalkers cannot fight Mutas and lings at the same time, Stalkers will be in a massive desadvantage to Mutas even with focus fire, the overkill makes it slower for the Stalkers, doesn’t matter if your Zealots win the ground fight if there are Mutas alive.
I know how dangerous mutas are to protoss (as are all air units to Protoss thanks to their horrendous ground to air). Not as dangerous as banshees imo but still very dangerous
All I’m saying is that stalkers do beat mutas, generally speaking. If the protoss player is not blind sided, and mutas come face to face with stalkers, then the stalkers win.
But when does that happen? Mutas fight the Stalkers in their terms, no Zerg player will ever engage Stalkers unless they are certain to win, the speed advantage will go to Mutas and Adepts doesn’t match it either.
Also, Mutas are far more dangerous than Cloack Banshees since Stalkers can kill them before they can retreat and the potential of 2 of them is far less lethal than 7 mutas.