If the watch was recently synced with the app to get current GPS ephemrides, it gets the lock within seconds. Otherwise, it may take much longer just like any other GPS device with outdated ephemerides.
Neither of your two statements coincides with my experience at all.
My garmin watch needed to be synced every time and it was always slow, and my garmin GPS on my motorcycle was the same. For example I once remember it trying and failing and eventually succeeding to sync during my walk from the tube through the parks to work one morning and then trying and failing and staying failed during my walk from work to the tube that evening. I was wearing the watch the entire day, so there was no possibility of it losing lock or whatever other than the obvious, which is it is just a really terrible device. Before I ditched it entirely I totally gave up on any gps functionality - it just was too high friction for too little payoff.
Secondly literally no other GPS device that I own has a noticeable “sync” or “lock” at all. They all use reasonable heuristics to get started and then improve their resolution as they go. If they ever lose GPS lock I don’t know about it except maybe a “map glitch” where I seem temporarily to be in the middle of a building instead of the street outside or whatever. The garmin takes ages, frequently fails to sync and sometimes also loses GPS lock while I’m doing an activity, and when it does that it ditches progress and pukes in the most inconvenient way possible.
I’m not in the middle of nowhere and there are no tall buildings near me. I am in London in zone 2 so there is exceptional coverage as you would expect.
If the watch was recently synced with the app to get current GPS ephemrides, it gets the lock within seconds. Otherwise, it may take much longer just like any other GPS device with outdated ephemerides.