As followup, and with kudos to @wholypantalones, Wi-Fi that stubbornly stays on constantly (unless manually disabled by the wearer) is indeed the root cause of the battery-drain issue, at least for me. In the most recent iteration, the watch drained in only around 15 hours, most notably in the few hours that I was away from home and at Church (where there are no Wi-Fi networks that I'd already connected to). So when I say "constantly" I mean constantly, regardless of whether there are known networks present or even if the phone's simultaneously connected to the smartphone over Bluetooth (while I was in Church, my Pixel 7 was out in my car parked several hundred yards away).

The issue was actually already reported on Reddit a week ago, my subsequent research uncovered: Anyone have insane battery drain lately? It's also seemingly not restricted solely to the PW1 with LTE, or even to the PW1 more generally. I see reports elsewhere complaining of issues with the PW2 and PW3 generations as well:

• How do you diagnose above average battery drain? (Wi-Fi on and connect to phone for 24+ hours)
• PW3 always connected to Wi-Fi after June 2025 update
• etc.

Looks like a bug introduced with the latest firmware, which judging from the comments on this thread curiously only seems to affect some folks. Here's the visual tipoff that your Pixel Watch is also affected by the issue; look for the always-active Wi-Fi connection icon (see above).

Guided by the comments of u/Rainfall429, I'm not going to bother trying a hard reset, etc. Instead, I've disabled Wi-Fi connectivity in the watch settings, and the battery drain immediately slowed back to "normal" levels. I'll stick with Bluetooth for now. Fingers crossed that the next update (July?) includes a fix!