The ability to prevent an extension from accessing specific sites is an improvement as long as the user can control it and it is not used for centralized access control.

The reason this feature is there is that many extensions play poorly with or should not have access at all to specific sites. For example, Grammarly has no business accessing a corporate billing system and IT might want to disable access. In other cases an extension slows a site massively and a user might want to say, "not that site" to an extension. This could be the start of a big end-user improvement, especially if it can be managed by users and installers.