You are basically right in your observation. But there’s a bit more to it. In addition to SolidProject and Inrupt you have the Community. These are the people on the Solid forum and circling around the ecosystem. They all have OSS focus and some create FOSS and also an independent German community branch has been created. Problem is that both from the SolidProject as well as from Inrupt until recently there’s near zero interest or time to build a vibrant community around the technology.
This has been discussed in a number of forum topics before. This might now change by the efforts of new community manager Marrelle from Inrupt who has also started an Inclusion team. I made two recent rallying cries for community to organize themselves: Should We Look for the Killer App for Solid? and Poll: Are You Satisfied With Current Community Engagement?
Why? Because I think it is very important for the technology. And because the Solid community is also the go-to place to ask about Linked Data on which AS/AP is built, we are complementary technologies. Unfortunately I have the feeling that Solid and AP/Fediverse are diverging rather than getting closer together. See also recent topic on Interop: Solid Application Interoperability Draft - Presentation videos and Solid, ACL’s and the future.