If you want to merge your code into someone else's repository, thereby benefiting from their continued maintenance efforts, how about you give them the copyright? You don't have to if you don't want to. You can keep your copyright by merging your improvements into your own fork and maintaining it yourself. It is within your power.
Seems like a fair deal to me. Everyone gets a nice AGPLv3 project to hack on. That's freedom and it is assured. If you want someone else to maintain that project for you the least you can do is give them control over it by assigning copyright. It's still AGPLv3 for everyone else, and it gives the maintainers the leverage needed to negotiate deals with corporations.
Companies paying for exceptions to the GPL is something even Stallman promotes.
https://www.gnu.org/philosophy/selling-exceptions.html
This is a good thing and strengthens free software. Being against this is a position so extreme that even Stallman rejects it. And it can't be done if you need the consent of every single contributor.
I even emailed Stallman directly to confirm the ethics of this. He says it's better this way because only the copyright owner can do it. Permissive licenses give everyone that power. Copyleft keeps it contained.
> It is my understanding that as the copyright holders
> they have the right to do it without any problems.
> They leverage the AGPLv3 to make it harder for their
> competitors to use the code to compete against them.
I see what you mean. The original developer can engage
in a practice that blocks coopertation.
By contrast, using some other license, such as the ordinary GPL,
would permitt ANY user of the program to engage in that practice.
In a perverse sense that could seem more fair,
but I think it is also more harmful.
On balance, using the AGPL is better.