The GPL very much restrict derivative works. It's the whole point of the GPL. "Usage" in the context of the GPL does not have the meaning you are using.
It is way more nuanced than that. For example if you never redistribute your work that was a fork from GPL code, then GPL states it's ok to never give back the source.
What we both said is compatible and consistent. The derived work is restricted by the GPL's provisions. Those restrictions just don't require you to distribute the source on demand unless and until you distribute derivative works to other users.
