Of course you can just disable javascript in your HTTP browser. But as the author states, it's easier to write a completely new client than to disable all the bloat in e.g. firefox.
Screen readers handle Gemini just fine - one of the clients I've tried outputs text and buttons in a GTK window, another literally just outputs text into a terminal and takes command line input, if a screenreader couldn't handle that I'd be horrified. The format is paragraph-based, there's very little styling, no guessing at what the main content on a page is.
I think screen readers can read text pretty well, also, since you've declared that to be a goal for some reason.
It's a waste of time compared to just making something new. That doesn't mean that normal browsers couldn't also get gopher support for those not interested in a lightweight browser.
You cannot do anything lightweight with a browser supporting, and itself being written in, web technologies.
Fragmentation is intentional. Although, nothing stops a web browser from also gaining gemini/gopher support. Just won't be "minimal".