If that doesn't alleviate your concerns or you disagree, I'd love to hear your thoughts about how we can improve
No single entity should have that much power, especially no venture-capital backed one.
You might want to look at the comments in this thread [1], to get a feeling of the "accusations", as you want to call it... I'm not "accusing" anything, I really couldn't care less, I don't use Vercel/Next.js and never will, but maybe you should read the linked thread, too see how people (at least on HN) see your company.
Personally, I don’t bother with nextjs at all.
A Next.js project can be deployed to a Docker image very easily [1]. If you want to use a provider that has their own infrastructure setup, then yes you need to do some work (that OpenNext does for you). But that's true of practically any framework deploying to a host that does more than just serve the docker container.