Depends on whether the important components like the CPU and their connections are intact. I remember that video from "waterjet channel" where they cut a hole in the middle of a Nintendo Switch and it still worked because the hole ended up entirely through the battery.

Or, it's impossible to tell whether it still works without looking up the internal layout of this iPhone model, which I'm too lazy to do.

It doesn't look so. I'd approach it in a different way: what is the biggest bite size you could cut out while still having an usable phone? You'd need to play not just with the size but also with the position.

But even though I have a box full of old iphones with broken lightning sockets I would prefer to find another use for them.

I don't think so, those first generation iPhones are not water-proof

Sometimes you can get away with discharging the battery, doing your wet work, and then drying very thoroughly before applying power again.

Yes but has 1 fewer CPU cores and less RAM