I acutally see the reduced burden that comes with actually sharing resources.

To extend the previous analogy: Valve didn't make desktop Linux viable on their own. A lot of it is owed to another self-interested actor -- Google -- through the reduced need for dedicated desktop apps (largely pushed by Chrome), and various enhancements to wireless and power management that were necessary to make it a viable mobile platform (directly benefiting Android/ChromeOS, but then spreading out to laptops and mobile devices in general, including handhelds like the Steam Deck).

You can see it on a smaller scale in ecosystems like Android -- where handset makers regularly contribute features from their UI skins upstream, so that they no longer need to spend engineering resources maintaining distinct versions of theming engines/notification badges/multiwindow/various other stuff.

On a related note this is an argument for open source models, not just open weights. I think a lot of the diminishing returns relate to the opaque nature of most models.