Of course, a vo2max doesn't explain everything as an endurance athlete. As a cyclist it has a big correlation to FTP, but there are also different metrics to be good at. Short sprints, recovery after bursts, plain grit for multi-hour rides etc. are all different skills not shown in a single number.
Example: if your real max is 60, but your watch says 50, you may be wondering why hard training isn’t increasing it.
Another example: if your real max is 35 but your watch says 45, you may misinterpret the signal when it jumps to 55 relatively quickly after a few weeks of hard-ish work.
Plus, if the value is significantly inaccurate then who knows what else is inaccurate about it? I appreciate that Apple have put effort into making it accurate.
I suspect for me and probably many others in the "acceptable fitness level" category the main factor influencing what ends up being reported as VO2max is stress, both physiological and psychological. That correlates real good. At least for me.