And guess what, when a corporation uses Elasticsearch in a serious way they will inevitably end up contributing back. It's actually easier to just get a change merged upstream rather than to manage a whole fork, unless the upstream is really hard to get patches merged with.

The whole narrative of "company X is offering Elasticsearch as a service and not contributing back!" is ridiculous. First of all, the whole point of free software is that somebody somewhere is going to be making money with that software, and that's okay, regardless of contribution. Second of all, in practice companies like Elastic will always exaggerate the extent to which corporations aren't "contributing back".

What they really mean is Amazon isn't contributing financially to Elastic Co. That's what they're pissed about, and that's why they clearly wish they were actually in the business of proprietary software (which they now are)