A handful of thoughts:

The universe of WearOS is likely to have a calculator app, out there somewhere. It's also fairly straightforward to build your own. Alternatively, most "smart" devices support speech input, which helps for the occasional calculations.

Speaking more broadly, I've had some sort of smart watch since the start of WearOS in 2015. I'm currently wearing a Garmin Fenix 5S+ from 2018. It's less "smart" than the Apple or WearOS watches, but gets a week of battery life, even after five years of daily use.

The true killer feature is simply getting your text messages on your watch. And that's not even the really killer part of it. It's that all the social cues around looking at your watch still kinda fit. Like, you're signalling that you're taking your attention away from someone you're talking to, without the level of disengagement that comes from staring at your phone.

Alternatively, if you're going for nerd cred, it's hard to beat a Nixie tube watch (e.g., https://niwa.watch/) or even a classic digital watch (e.g., a $20 Casio: https://www.casio.com/us/watches/casio/product.A158WA-1/; similar guts are also available as a G-Shock model with solar charging and atomic clock radio time sync).