Yeah, `git request-pull` is only a helper to create a pull request, while GitHub/GitLab/etc include that in addition to a (convenient) vendor-specific way to track received pull requests and a code review web interface.

Initiatives like ForgeFed are trying to define a more neutral way to share this information, but I don't think there's any estimate date for when there'll be an actual implementation of it. If that ever happens, it'd be possible to get vendor-neutral tooling for that kind of collaboration.