Custom matching algorithms and ability to fine tune or expand matching algorithms according to new content blocking challenges are actually a kind of advanced feature that are used by all those users without them ever realizing it since their content blocker work seamlessly on their favorite sites without the need for intervention.
The declarativeNetRequest (DNR) API has been quite improved since it was first announced and its great, but since it's the only one we can use now, it's no longer possible to innovate by coming up with improved matching algorithm for network requests.
If the DNR had been designed 8 years ago according to the requirements of content blockers back then, it would be awfully equipped to deal with the challenges thrown at content blockers nowadays, so it's difficult to think the current one will be sufficient in the coming years.