Looks like you cleanly point out their violation of the AGPL. I wish I were a lawyer with nothing better to do, I'd definitely be suing the MinIO group, there's no way they can cleanly remove the AGPL code outsiders contributed.
I don't see a contributor licensing agreement (CLA), so you may be right.
(I personally choose not to contribute to projects with CLAs, I don't want my contributions to become closed-source in the future.)
I'm not a contributor to Minio. This is its own separate thing.
I do have a separate AGPL project (see github) where I have nearly all of the copyright and have looked into how one would be able to enforce this in the US at some point and it did look pretty bleak -- it is a civil suit where you have to show damages etc. but IANAL.
I did not like the FUD they were spreading about AGPL at the time since it is a good license for end-user applications.
I don't think there would be an issue with removing AGPL contributed code. You can't force someone to distribute something they don't want to. IANAL, but I believe that what (all?) copyright in software is most concerned with is the active distribution of code -- not the removal of code.
That said, if there was contributed AGPL code, they couldn't change the license on that part of the code w/o a CLA. AGPL also doesn't necessarily mean you have to make the code publicly available, just available to those that you give the program to (I'm assuming AGPL is like the GPL in this regard).
So, that I'd be curious about it is -- (1) is there any contributed AGPL code in the current version? (2) what license is granted to customers of the enterprise version?
Minio can completely use whatever license they want for their code. But, if there was contributed code w/o a CLA, then I'm not sure how a commercial/enterprise license would play with contriubuted AGPL code. It would be an interesting question to find out.