While individual components are being published as GPLv3, they're requesting, and getting, written permission from some contributors to re-publish the code under alternative licenses, at Canonical's whim. That is releasing licensing rights to someone else. Even if Canonical proves trustworthy (and they've not, due to their strange browser collection data practices), that goes far beyond most open source or freeware licenses.
Although I enjoy slinging mud, copyright assignments and contribution agreements are commonplace when contributing to larger free/open source projects.
Transferring copyright for example to GNU is mandatory when contributing, gives the project the flexibility to relicense in case an upgrade is in order (like GPLv2->GPLv3) and avoids having to hunt down all individual contributors in case a change in license is required. Such agreements are in place with Apache and Mozilla too.
All things considered, GNU would indeed be more trustworthy in my book than Canonical (if only because GNU doesn't have a commercial motive) but regardless when an "entity" does the bulk of the work I think it's fair to allow them the flexibility to relicense when contributing.
It is a different situation when the owning "entity" drops the ball and the community does the bulk of the work, but then the option to fork is always open. LibreOffice serves as a nice reminder that being able to relicense doesn't mean much if the community decides to fork and move on.