Going into a shop hasn’t necessarily been something people have wanted to do for the past couple years for obvious reasons. So getting hands-on can be a challenge/risk.
Size and dimensions might help if you already have something to compare to, but that’s also not always an option.
I knew the size of my iPhone X, but wasn’t sure if I wanted to go all the way up to a Pro Max or stick with the standard phone. Both would be larger than what I had. In my case, I have a 6.5” Android phone I used to guess, but when I got my 13 Pro Max, it was shorter and wider than the Android. So the Android really wasn’t a good device to go by, but it did give me a general idea.
You make it sound so easy to make the decision. I believe it’s more complicated for most people and currently has the added challenge of not as much access to hands-on.