[Andrew Bollard]

Not that simple. Quoting from the Evoke article on Muscular Endurance, regarding gym-based ME:

This Muscular Endurance workout is appropriate for Mountaineers, Mountain Runners and Ski Mountaineers. Anyone who needs to go steeply uphill faster for longer will see gains from this workout.

Further down:

While I generally encourage the use of weighted carries for mountaineers, I’ve used this a base period preparation block before moving to the weighted carries with a number of high level mountaineers and alpinists with great results.

So, it seems to me that the gym-based ME can be used either as a standalone ME program for people living in places where steep hills can’t be reliably accessed, or as a preparation for outdoor ME work. I fall into first camp; I would have to drive at least 2 hours to access a steep enough slope to do uphill weighted carries, and that just isn’t practical for me, so I do gym-based ME at home instead. That way, I can program it for a Wednesday, leaving Thursday and Friday for active recovery/Z1 sessions, and still have the whole weekend to do long hikes/runs/climbs.

In general, training recommendations are hardly ever black and white, this one vs that one, outdoor vs gym-based. You always have to modify it to suit your circumstances and what you can realistically commit to doing on a consistent basis. It sounds like you have the best of both worlds available, so you could potentially do a gym-based ME progression first to prime yourself for outdoor ME.