Going by how my Macbook's battery life evaporates with 10 Chrome tabs + Slack + Zoom, I believe it. Gaming is definitely less load than multiple windows of modern work apps.
Compared to playing a game which would definitely use both GPU and CPU, instead of mostly just CPU?
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.
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.
If your MacBook battery is recent and lasting for less than 8 hours, you’re doing something very unusual.