one of the "feature" of ads is that they track you in a cross website way. and as no having cookies & co, gemini makes this job a lot harder for an advertiser.
In addition, I _know_ that if I follow a gemini:// link I'm not gonna have to defend myself against aggressive JS or too much unpleasant design that I can't override, whereas you never have that guarantee on HTTP.
You can make an http web browser not store any cookies. This may limit the operation of some existing sites that rely on cookies though because they can't maintain client side session information or other state. Tracking cookies are not inherent to http. http is just the content transfer protocol. I feel like campaigning against tracking cookies within http, and advocating for http browsers to have more stringent handling of 3rd party cookies (like what Firefox offers, but maybe even more) is more likely to get wider adoption than coming up with a complete replacement for http.
Also most clients do not render images at all or only render images if you click on them. Very few clients support any kind of animations or sounds. Of course someone could still do marketing and post some text-only ads if they want to. If it is too annoying I guess I will not visit that page again. If it is not too annoying I can just ignore it and keep reading. An ad is not automatically a dark pattern.