>> As in, all modifications must be made available. Is that not meeting your definition of giving back?

Available to all users. Not previous authors. There may be overlap, or there may not be overlap.

Plus, I would say it's giving forward, not back. If there are public users then the original authors can become users and get the code. But there will be bug fixes and features smooshed together.

Which is why i posit that there's no "give back" concept in the license. Only "give forward".