> Even if they choose AGPLv3, the creator still maintains full freedom since they own the copyrights.

Only if they either refuse all contributions, require contributions to be made under an MIT license or similar (and then immediately relicense back to AGPLv3 before publishing), or require a CLA.

I'm all for personal projects to be licensed AGPLv3, but we must acknowledge that the moment you take others' AGPLv3 contributions, in practice you won't be able to do those other things.

Of course. The creator retains copyright. If there are multiple creators, things get complicated quickly. This is also why GNU projects ask that contributors assign copyright to the FSF. Gotta deal with this sort of bureaucracy before contributing is allowed.