The problem with the VO2max metric is that there is no measurement of it outside of a few lab methods, certainly not in a fitness tracker, so they're estimating. It makes more sense to look at the other metrics that it CAN easily measure, like heart rate recovery to get a quantifiable and repeatable measurement. I agree for amateurs accuracy is not necessary, but repeatability is. If I weigh myself today and the scale says 10 lbs below my actual weight, and tomorrow it's 10lbs above my actual weight that's a problem. If it's always 10lbs below that's fine, the delta will be correct. You can't say that for VO2max you get out of a fitness tracker.

My watch says my VO2max is 36.8 which would put me very strongly in the long term negative health effects bucket and well below average. Meanwhile Garmin claims it's 51 which would put me in the top 15% of my age group. It can't be both. They're just made up estimations, and following them blindly could be dangerous. What if someone's is going up even though they're not actually doing a healthy amount of exercise? Or someone's is going down or maintaining even though they are, causing them to fall into negative thought or behavioral patterns? Better to stick with some other data points