Whether those catastrophes could destroy present humanity wasn’t the point, which was whether or not near misses in potential extinction events have ever occurred during our past.
Consider it that way : under your assumptions of our world being more robust nowadays, what would count as a near miss today, would certainly have wiped the frailer humanity out back then; conversely what counted as a near miss back then, would not be nearly that bad nowadays. This basically means, by constraining the definition of a “near miss” in that way, that it is impossible to show any such near miss in our history. That is at best one step away from saying we’re actually safe and shouldn’t worry all that much about existential risks.
Speaking of which, when arguing the definition of an existential risk, and from that arguing that such catastrophes as a nuclear war, aren’t existential risks, blurs the point. Let us rephrase the question : how much would you want to avoid a nuclear war, or a supereruption, or an asteroid strike ? How much effort, time, money should we put into the cause of avoiding such catastrophes ?
While it is true a catastrophe that doesn’t wipe out humanity forever, isn’t as bad as one that does, such an event can still be awfully bad, and deserving of our attention and efforts, so as to prevent it. We’re talking billions of human lives lost or spent in awful conditions for decades, centuries, millennia, etc. If that is no cause to serious worry, pray tell what is ?
You’d think that’s actually pretty much what most of us humans care about.