Apple Watch acceptable accuracy?
I think this is totally expected it can happen, but not be the usual experience.

Apple has an article explaining how to start over in the calibration. If the measurements start off wrong - they won't get back to accurate in my experience and one watch I had didn't have my phone nearby when I set it up, and ended up with my step length 10% off.


https://support.apple.com/en-us/HT204516


I'd run through all the items from the top and see if you can get the step length accurate for the terrain you're most likely to want the numbers to be accurate. I've set up about a watch about a dozen times, and I only had one time it was off enough to need a recalibration, so it's hard to guess how common this is from anecdotal reports like yours and mine.