Interesting thread. I don’t commute on my bike and I’m not training to race so I have an allotted number of hours I can get off family stuff to ride each week. Riding to stay fit and because riding bikes is great.
Pre-strava I used to go and ride but I started to get fixated this time last year on miles in the bank. Basically stopped mtbing and just rode the CX on road to get the stats up.
All that changed when I my road bike was trashed and I was waiting for new wheels for 2 weeks recently. I went out on the mtb and really enjoyed it! So I’d say quantity and quality are both important. And I suppose I think miles isn’t a benchmark against other people, only for you week to week, month to month. My miles a week may be nothing to some people and loads to someone else, but it’s just right for me! (My goal this year is a weekly target of 60 to include one MTB outing!)