I mostly don't disagree with any of what you said, however:
Speaking only from my experience with REI, I agree with most everything that you said but I might change "doing whatever it has to do to expand, often while loudly protesting it needs to do so in order to further The Noble Cause" to "doing what it needs to do to survive in an increasingly competitive market and meeting the needs of the changing demographic".
And that gets messy. Original demographics age out and new demographics require some other product selection. Co-op members vote and are pretty damn loud. Climbing shoes change to golf attire, mountaineering tents change to family camping tents with a separate room for the kids, road bikes change to mountain bikes change to electric bikes, the "tippy" performance kayak changes to something that your Mother-in-Law can paddle.
It sucks. That we both agree on.
I think we agree on even more than that. My issue is not, and never was, with the changing offerings. As young people who were active backpackers and ski trippers become parents, of course it makes sense to offer them car camping stuff and kid-size sleeping bags. In an era when paid time off from work is decreasingly the norm, and outdoor rec pivots towards shorter duration/higher intensity activities, naturally you need to stock trail running shoes, SUPs, and yoga pants. And as old farts like me get creakier and creakier, sell us the thickest, cushiest sleeping pads you can source.
My beefs included how our buyers' ("Product Managers") success was measured. Not on overall member satisfaction and on the value-for-money of the individual products offered (which should be critical metrics of how a retail co-op is serving its owners), but on the easier to measure total value of goods sold, the margins made, and number of "turns" per year or quarter.
At the executive level, success was measured by total sales and by the rate of growth ("Go big or go home.") As with any other counter-factual/alternate history, it's impossible to know for sure, but I believe that if MEC hadn't been so over-extended by the growth-for-growth's-sake approach, it might well have weathered even the COVID crisis, and still be a co-op. Perhaps not as big as some other outdoor rec retailers, but the regular capitalist market creates a never-ending supply of those. A member-owned retailer was a welcome novelty that, when it was still true to its principles, benefitted even those who never shopped there: Other retailers knew they had to match MEC's lower margins on commodity items. MEC really did, to use that over-used phrase, disrupt the market. Its mutation into a regular, for-profit retailer is a loss to all.