An open source project can be built upon and extended by anyone, and that includes its creators.
We don’t say that an open source project is diminished because some third party productizes it and makes money. PostgreSQL is not diminished by neon or rds.
No, we continue to judge the project on its own merits. If it continues to offer value, to be compelling, well-supported, and stack up well against alternatives, then we keep using it. We don’t think “it doesn’t have all the features of rds, so screw postgres”.
If the commercial side of the project takes away from the oss side and the oss project goes downhill as a result, then that certainly is a frustrating and disappointing outcome. But when both sides are thriving, it’s a fantastic win-win.
The maintainers get to focus their full attention and passion on the project. The community gets better and better software. And people who are willing to pay for advanced or niche use cases get their problems solved too.
Summing up, the problem is not with the whole model of open core, but with specific projects and companies that get it wrong.
There’s no fundamental reason why the oss side and the product side have to be at odds. It’s just freemium, and there are countless successful and beloved freemium products out there who figured out how to get the balance right.