I'm puzzled by this article.
It criticizes the open core model by listing some hypothetical ways that it can skew incentives, but completely ignores and delegates to a footnote all the success stories it has made possible. It's missing the entire point of why open core, _when done right_, is a good thing for both users and the business.
In the case of sanity.io, how is it beneficial to the user that the editor is OSS, when their data—the most valuable part of a CMS—is kept behind a proprietary service they need to subscribe to? It's using OSS as a hook to get users tied into a proprietary product.
Secondly, the source available model is indeed not open source, nor, more importantly, free software. Users have no assurance that the software they're using is actually built from the source they have access to. Crucially, they have no rights to modify, distribute or even build the software. This is the antithesis of free software.
Releasing only OSS components is also hardly useful. Sure, developers might benefit from using certain libraries, but the core value of the full product remains locked away. There is no incentive for companies to keep developing these components, since the business doesn't rely on them directly.
All of these approaches are much inferior to the open core model.
When done correctly, with an open core, users have access to a _fully functional and featureful_ product that exists standalone as free software. Only certain features, typically intended for advanced users or enterprise customers, are offered as a commercial product. This can be accomplished in many ways: cloud SaaS, commercial extensions, priority support, etc.
The crucial aspect of making open core successful is that the OSS product should be, as the name suggests, _core_ to the business. This way the incentive will always be to develop this component, which will benefit both your OSS users and paying customers.
There are many companies who've done this successfully: GitLab, Elastic, Redis, Hashicorp, Grafana, etc. These are loved by OSS users and customers alike, and they're certainly not "relatively new in the grand scheme of business".
The reality is that open core is the most successful model to make free software sustainable. There are far too many projects that failed because the developers weren't able to monetize them properly. It's worth celebrating that we have as many successful OSS projects as we do today, and in large part this is thanks to the open core model.