My Pixel 3 is small and I can text and hold it using one hand with no problem.

https://store.google.com/us/product/pixel_3_specs

I think people just have different standards here, which should be no surprise (different hand sizes!). I found the Pixel 2 (and 4, which is nearly the same physical size despite the larger screen) to be tolerable, but nowhere near ideal. I like to one-hand my phone, often feel like reaching for things with my thumb comes close to a hard drop to the floor.

I think my sweet spot was the old Nexus 4.

Sadly not actually small. I have a Pixel 3A right now and I hate it, it's way, way too big. What I need is something where I can reach the top of the screen (notifications, Firefox URL bar and tab controls, other controls) while using one hand, without loosening my grip on the phone. This worked fine up to about 4.7" screens. Beyond that and it's just impossible.

Agreed. I happen to have my old Moto X handy; I stuck it to my fridge to access OurGroceries, and it's still working fine at the ripe age of 7.

The 3A is nearly an inch taller than the original Moto X: https://www.phonearena.com/phones/compare/Motorola-Moto-X,Go...

As you say, that makes it awkward to use the phone one-handed. I'd definitely buy something more the Moto X size if it were otherwise equivalent.

I use the Firefox Preview Nightly that provides the option to have a bottom URL bar.

I wish notifications and controls where down to like they are in my KDE.

Go to GSM Arena and plug in your max dimensions. Leave the screen size alone since modern small bezel phones pack more screen into a smaller package.