That is effectively the case. See for example DDIO with Intel which can only be enabled for specific devices with full cooperation between Intel and this particular vendor.

You cannot compete with a DDIO-enabled device, which of course all Intel devices are.

See also the Intel multibuffer crypto library, which was specialized and timed for Intel CPUs. No one else could write at this level of optimization, because we do not have the internal design and simulator that Intel work with.

So yeah, you are talking with sophisticated hardware which will have firmware blobs and undocumented features. If you only rely on general instructions sets you will only get so far. When we are talking about ns of latency and these level of bandwidth, they make the difference between several stacks.

The push for smart-NICs will increasingly blur the line between soft and hard layer. We can either direct our efforts so as to avoid rewriting an abstraction layer upon it or do so for each vendor-specific API (OFED is but one example, there will be others).