You are not wrong. Browsers could standardize the information exchange and approval that happens for cookies and then implement a sane UI for that similar to how e.g. browser location tracking requires opting in. That should be a perfectly valid alternative for home grown UX that website developers add themselves and offer a better UX.

To do this you would need to provide the legalese for that in some standardized way so the browser can pop up some UI that allows users to review that and approve/reject that. It should simply refuse any kind of cookie until the user has approved. That approval should be removable as well. Part of that should also cover having a sane API around that so sites can decide if they need to fall back to displaying their popups for this. Browsers that support this could even start defaulting to block all forms of cookies until explicit permission is in place for a website, regardless of existing UI. Many users have extensions that do this.

Wouldn't be the worst idea. Of course the flip side is that it also makes it easier for users to say "no" a lot (I would). And there is the notion that this may be a grey area under the current legal text. And of course some browser vendors have vested interest in the whole cookie & tracking business (Google).