What's going on my phone that it grinds to a halt? Why does a factory reset sometimes help, but sometimes not?
It can't just be that the workloads are more resource intensive. If I go get an old tablet it will take 5x as long to load google.com as the day I bought it.
Once upon a time, google.com was like five lines of HTML. Google loved to brag about how they didn't even close their tags, because the page still rendered and it saved bytes.
Now I measure it at 300+ lines and 200KB, not counting assets.
Same generally goes for every software you know and love.
A resets might improve performance of the flash device if it frees up additional space or does something similar to an SSD "trim" event.
If you take your 5yo tablet and load the 5years younger OS, a 5years younger app or a 5 year younger version of google, those are designed to be "usable" on modern hardware, and "just bearable" on your older hardware. So it's not apples to apples then. You are running an app (or page) that is much much fatter. And yes it even applies to the google front page.