> Nothing about the web implies heaviness
Yes, except that heaviness is allowed, and lightness is opt-in.
> you’re also free to use e.g. Lynx/w3m/elinks browsers to browse the modern web or the subset that renders well on it.
Yes, except you have no way of known if and when something you want to search for will work on these. Whereas anything on Gemini will work on Gemini.
Ultimately to some extent it's an anti-bloat guarantee. Yes not all of the normal web has bloat, but that's not the point. To use a Genetic Programming analogy, it's the difference between not even considering program trees beyond a certain small size, vs having elaborate strategies for countering the inevitable program of bloat once you start dealing with programs of sufficient interest and complexity. But if you want to end up with programs that only consist of less than 10 instructions that you can reason with easily, then perhaps a "small world of small programs" is exactly what you want. And the natural content that fits this "small programs / small world" guarantee is personal thoughts and atomic websites. Which makes for an interesting webspace.