The Zenfone is still significantly larger and heavier than the iPhone mini, which for me is already at the upper limit for one-handed use.

Bit larger yes, just under 1oz heavier... not too significant. And headphone jack, no notch (dealbreaker in 2021), no CSAM.

I already found the increase in size and weight from iPhone SE (2016) to iPhone mini quite significant, so... YMMV.

it's not a "bit":

Weight and Dimension 169g, 148 x 68.5 x 8.9 mm

thats a full cm longer than the 2020 SE, which is already bigger than the mini. it might be "an answer to the mini" in features and spirit but not in size by far.

A notch just makes the screen slightly smaller. Why is that a dealbreaker when you're already asking for a smaller phone?

Apple dragging out the notch removal as long as possible. When they finally do (next year?), notch devices will look/feel like old trash.

From a quick look at tech specs from a few sources (asus, gsmarena, etc.) the USA version lacks 5G band n41, which is the backbone of T-Mobile (+Sprint).

Recently spent a long time agonizing over getting a new phone. This is the only phone that checked all my boxes (small, decent ram, storage and camera, headphone jack...) but it doesn't work on Verizon :(

Went with the Pixel 4a, we'll see how it goes

4a is a great choice. I think you'll be happy with it. The Samsung 10e is another similarly priced device. I think the Google photos integration is really nice. Even though the Google photos app drives me nuts sometimes.

How's battery life? I think it's not great, is it?