What's the difference between

maven.mavenContent.includeGroupAndSubgroups

vs

exclusiveContent.filter

in RepositoryHandler/repositories?

Iirc, with include, you define what is found in that repository, but it could still be resolved from a different repository too, with exclusive content you say that it is only to be taken from that repository not from any other.

Yep, with include you limit the requests that will be made to that repository, irrespective of the others. With exclusiveContent you limit the requests that will be made to other repositories (because they'll only be made to that repository)