I think that's the wrong comparison, because companies like Redhat are pretty much by design forcing down margins in the spaces they are operating in by lowering the bar to compete. E.g. to compete with Redhat, you can start by learning their products and offering consultancy services on them, and then gradually forking each one of them to offer specialised products; but conversely so can everyone else.

We should not expect to see open source companies get to Oracle sized valuations; instead we should expect to see them chip away at the market share of companies based around proprietary software until said companies margins shrink, and either their valuations shrinks with them or they expand into new areas in time to delay it.

But ultimately we should expect larger and larger parts of the software space to be commodified and margins driven down for core features like this.