It’s a fascinating situation, really: this kind of asymmetry (AGPL for you, but not for us, even if you contribute) is antithetical to the purpose of the AGPL, but desirable for the leaders of quite a large fraction of projects that choose the license (to the point that they might either not use the AGPL or not accept contributions if they couldn’t do it).

I think a CLA that says "You provide us with an additional license to re-publish your code under any license we choose" with modifications to limit attribution, might work. That way the code is perpetually AGPL, but the company is free to offer derivative works under other licenses. Hence you can always use your code, you can fork, you can do all you want, and the company cannot take the code, as it stands at that point, away from the public.