@mrkvon I have had extensive discussions on this forum before, along similar nature of your two bullet points. I too find the specs to be seemingly overly complex, maybe too academical… idk. In the past I’ve made remarks on the positioning of the Solid Project as a whole, which was very confusing to me (this has since improved somewhat), on the need for simplifying organization structure and ceremony and focus on building a strong community.
At the outset of 2019 I felt that The biggest challenges for Solid are not technical in nature, nor are they in spec writing. And I still feel this is true.
But it may also be that Solid is following a wholly different approach to making both the standards and technology ecosystem a success. There’s much focus on commercial viability, and the parts of the process where customer feedback is gathered and their needs are analysed (which is even more important imho than “spending time building things”, which comes afterwards) may not happen all in the open but at various boardroom discussions where representatives of Inrupt and other companies sit at the table to flesh things out with prospective clients. And codebases may sit in private repositories until the time they may or may not be open-sourced when these companies take a leading role and release what they hope will be killer apps.
This is all speculating, of course, but might be a valid strategy from the companies’ perspective. Having full control over the specification process (unburdened by W3C slow-going process, and big player influence (see DID-Core issues)) and technology development (early adopter access), not-yet-building strong open community in early spec stages (at the cost of losing active members)… all this enables core participants to be fast-movers, possibly gaining competitive advantage (competitive to competing specs? to fast market developments? Idk, again).
If such or a similar strategy is indeed followed, I still think it is very high-risk in terms of eventual success. Still convinced, as I said in 2019 that much hinges on: Changing perceptions of the technology and gaining [widespread] adoption.
Update:
Re: Comparing competing (?) standards…
Though - just like for Solid - I only follow it at significant distance (and without any interest for the blockchain parts), the whole standards approach of the Decentralized Identity Foundation (DIF) has a certain appeal to me. From an early draft on Encrypted Data Vaults to a draft specification of Confidential Storage to early-bird implementations, I found all the work clearly positioned, and intuitively documented in easy-to-understand ways. Note, this spec is just one node in a large verifiable credentials specifications map. Note too, that hey still have a lot of work to do on the Interoperability side of things.
Overall the positioning, clarity of message, documentation and objectives, and community engagement are imho key success factors in any such efforts.
BTW, in the case of DIF the many links with Blockchain technology may be hampering adoption, while for Solid echoes and associations to the prior Semantic Web hype cycle may be inhibiting factor.
(@NoelDeMartin sorry, I realize that this side-tracked your topic with only slight reference to interoperability, while responding to @mrkvon’s two points. If you want I can transfer to a new topic and cross-ref (then DM me, so as not to pollute the thread further 
))