No specific thoughts on the Arroyo, but I have used the Marmot Hydrogen and Helium before "upgrading" ("sidegrading"?) to the WM equivalents, the Megalite and Alpinlite. The Marmot bags were the best I'd used until then (including a 1980s TNF Blue Kazoo, back when North Face was the Gold Standard), and I had no complaints.

The biggest difference I found between them and the WM bags, strictly based on perception and not objective measurement, was rating accuracy. The Marmot bags seemed to be pretty much dead on with their ratings - a 30-degree rating kept me warm at 30, but left me chilly at 25. The WM bags seemed to be good for another 5 degrees: at 25, I was still warm in a bag rated for 30. Also, the WM bags just seemed a bit more "deluxe" in the detailing, while the Marmot was just a fundamentally well-made bag. I can't point to any specifics for this; the WM bags just felt more luxurious when I climbed in them. As I recall, for similar ratings, there was no significant difference in weight or compressibility between a WM Extremelite series bag and a Marmot Element-series bag. In the end, I just like WM better, for no objective reasons.