I just switched from a OnePlus 5 to a 9 Pro a few weeks back, and it is a noticable improvement. But you are right, while I was on the 5 I thought performance isn't a problem.

I have a One Plus which is slightly newer than that (~4 years old). It's very slow. I suspect people with a sentiment like yours just don't care about small amounts of latency. I wish the screen was immediately and instantaneously responsive to all my actions, and I wish all the apps I opened would immediately be interactive as soon as they are visible.

I had one but the battery was dead and could't find a replacement. With a Pixel 7 Pro now I feel the speed difference.