I’m concerned about all privacy angle of this personal information vacuum device category. What are the recommended privacy focused alternatives?

Also a smart watch without firmware updates seems like an infection spreader?

You can use this with GadgetBridge if you're concerned about your privacy.

Given the small amount of memory and its inability to run 3rd party code, I'd be staggered if this could be used as a vector for anything. What's it going to do, spam ignorable BLE messages?

There's a category which is unbelievable it doesn't have as much popularity on open protocols/oss support which is a killer feature for these kind of wearables: glucose levels tracking with reverse engineered vendor lock-ins (think of Abbott sensors, etc).

I’ve never understood the value proposition of a smart watch for that reason. It seems mostly a fantasy thing based on having been conditioned by movies all their lives. Even the primary use case as a fitness tracker does not make any real sense; because as a beginner through novice, you don’t need to track minute details, it’s about simply getting to a consistent habit, and as an advanced person, you get nothing more from what a watch can track than you would from simply performing your routine and maybe timing yourself and journaling, which has its own separate benefits that are lost with a “smart watch”.

Given all the negatives (to users, not to the corporations you become a harvested product to), it simply does not make sense to have a smart watch, aka a tracking bracelet.