Telling people to guard preemptively as a counter to miracle of nature doesn’t make any sense. There’s too many situations where you’re in a moderate danger of getting hit by it if you’re involved enough in the fight to be useful to your team and not griefing them. You can’t just guard just in case all the time since not only are you not doing anything else during guard, in higher ranks randomly wasting your guard puts a giant target on your forehead that says “free easy kill if 3-4 players swap onto me”. Which they will.

Guard a lot of the time is a reactionary measure when you start seeing damage come in or you’re otherwise in danger in a telegraphed way (rooted inside magma ball aoe is a common example) and is only a proactive measure in select cases where you’re very very clearly in danger of getting focused due to positioning/lb/playing aggressively to secure a kill