They're both rare occurrences. Saying one is rare doesn't make a compelling argument in favor of another. Either one "can" make the difference, but the one with a higher expected damage output will make the difference more often.

Crit is just a percentage multiplier on damage. I don't know how you could possibly argue this point, that's literally the definition of it. A 1% chance to deal double damage is functionally the same as a 1% flat increase in damage. This is just a mathematical fact. To put it bluntly the bit about "not nearly enough auto attacks to average the damage bonus" makes... no sense.

There are situations where marginal increases of AD are useless and crit is useful, and vice versa. Neither of these situations is inherently more likely than the other, and the unbelievably large number of circumstances that can lead up to a kill (or a missed kill) essentially makes either outcome random. So a smart player will build to maximize expected damage output because that situation will come up more often.

I don't know why you're mentioning crit normalization. It has literally no bearing either way because it also reduces crit chance if you crit recently. All it does is bound the effect of variance, which (if anything) is an argument AGAINST picking crit, because if you were choosing crit because your champion can somehow uniquely capitalize on damage spikes, then normalized crit makes it very hard to chain multiple crits in a single damage window.

I don't know why you mention jungle clears being easier with crit. Compared to nothing? Yes. Compared to AD? No. Crit, by design, scales harder into the late game than the early game. Choosing crit over AD is impairing your clear. Again, this is just a mathematical fact. You're choose a multiplicative increase in damage output over a linear damage output in the early game when linear damage increases are more important.

I'm not really sure why you're arguing this. These are just objective facts. Trying to argue otherwise is like trying to argue that the sky is green and that the sun is made out of tuna.