But I think even the idea that "Gemini can replace web pages (blogs, news posts etc)" is wrong. Gemini presents an alternative, for when you want things fast and simple, and for when you want to be sure that every page will be as fast and simple as the next. And yes, as you mention, for when you want to tinker and explore in a cool new space.
I don't think Gemini is supposed to make "dev life any simpler", or "decrease the scope of the web". It's just something new, something different, that some of us have taken a liking to, each for our own reasons.
To use your analogy -- Gemini isn't a bike while the Web is a car. Gemini is a pedestrian. There's great value in walking, but I wouldn't want it to be the only mode of transportation.