The modern web is pretty taxing on a GPU... Plenty of webpages have 100+ layers to composite together...

Sure, but those only get rendered when stuff is actually changing on the screen, otherwise it stands still, compared to games which would (usually at least) continue to render N FPS no matter if the screen is identical or not compared to previous frame.

Almost every such app uses GPU as well.

True, but nowhere near the level that a game would. As an example, it'll be hard to find a productivity/office application that is bottlenecked by the GPU, while for games, it's relatively easy to find.