Maybe some of these other metrics you just need it to be consistent. Even if its consistently wrong. So as long as your own watch/device keeps giving you (incorrect) data, if its always relative maybe thats good enough to work with seeing longer term progressions etc. Wrist-based heart rate on the other hand, as I keep seeing myself (when my HRM battery dies), and often read about, is inconsistently wrong. Which is just the worst of both worlds. And basically useless.
