yeah sure, but thats for every race the same. if the opponent does strat a, you need the counter to strat a, unless you wanna lose. if you see mutas right ahead and have a cannon/sb ready, you wont take much dmg from mutas. you most likely have a stargate in your bo, so you dont even need to invest ressources to additional buildings, you can, since 2stargate is a good response to mutaplay.
for scouting, stargate and robo is same effective. stargate has the advantage of clearing overlords tho. but with oracle or even voidrays, you shut down any allin completely, while with robotech, you still can mess up. so stargate is more bulletproof against allins in general, since nothing from the zerg can shoot up (if he has queens with it, its another story).
if you compare it - yes, its easier for toss to scout for tech than it is for zerg/terran against toss. toss can proxy his tech all over the map. with zerg, you have a huge radius of creep around it, so you dont even need to exactly scout the building. its enough if you see the creep, to know, that somethings there.
archons help to survive until you have cannons rdy. it needs a certain amount of micro/awareness, to load/unload the prism with archons yes, but again, if you didnt scout the spire tech, its your fault.
and zergs arent just blindly preparing for everything. atleast not, if we talk about pro lvl. and if he prepares for everything, he allrdy takes dmg, without you doing anything to him. 3 spores alone are a big investment. if you build 3 spores to be safe against oracles and then, a 2base immo/chargelot attack hits you… gl by definding that.