But I still believe all those other factors have significant roles.
But this would be true of longer term changes as well, but I guess what you could be saying is that if you notice a change on a daily basis, then you're more likely to attribute it to diet, rest, etc than noticeable gains over the course of one workout.
I'm not of the same mindset. I think noticeable changes can happen rapidly. The point of the question was in reference to the theory of "microtearing". I've started a couple of threads on here before about how I don't believe it actually exists. I was at the gym a few days ago and in the locker room some guys were discussing a certain arm routine and one of the guys said he can always tell by the day after whether or not a routine is worth sticking with- in terms of appearance. For me that's usually been the case, too. Not necessarily monstrous gains in a day, but I can see some change pretty quickly and I think it's a pretty common experience. If microtearing really existed, I think it would be more common to notice changes several days after you've trained a bodypart. It's possible that there are people who do experience this, but as I thought about it, I don't think I've ever heard or read anyone say that.