The transitions never get press or notice, unless they are bad. Then you get comments about how it looked "unprofessional". Apple keynotes are a great example -- they will never have a slide without a transition of some sort (the instant replace that you mention).
I get paid to make presentations, I've worked with other paid speakers, and I've seen 1000s of presentations. All the people who get paid to make presentations use transitions (and almost all of them use Keynote too), and there is a reason. Because it just looks "unprofessional" when you don't.
This book really upped my presentation game, and using transitions is in it with more explanation, if you're really interested:
I get paid to make presentations, I've worked with other paid speakers, and I've seen 1000s of presentations. All the people who get paid to make presentations use transitions (and almost all of them use Keynote too), and there is a reason. Because it just looks "unprofessional" when you don't.
This book really upped my presentation game, and using transitions is in it with more explanation, if you're really interested:
https://nealford.com/books/presentationpatterns.html