I'd say the shift to mobile went through a similar arc into decline as the web, actually.

Newgrounds really was the golden age for web gaming. And, similar to early web, early mobile gaming also started out with nostalgia-worthy charm and heart. You're right that it's been hollowed out, but the same thing happened to web gaming after the Flash era. The social casino era is maybe its 6th reinvention, and its lowest yet.

Now that mobile gaming has been raced to the bottom and consolidated (and thanks to the dual tailwinds of AI making it easy to write code without engines and the web maturing in its 3d+networking capabilities) we're started to see a resurgence of web-based games - it's my full-time job now! Granted we still do rely on mobile apps (as web wrappers) for monetization, but that wall is crumbling rapidly.