You are talking about game engines and their complexities, which makes it hard to comply. There are compliant full fledged operating systems out there (I am sure you have heard of a few) that are actually "open source". So I am not sure why any company should get away with using the well known term in a misleading way.
Let's talk about the operating system angle. When I went to work at NeXT in 1993 there was a lot of GPL code in the system. By 1999 as Mac OS X approached release there was a frantic effort to remove all GPL code in favor of BSD or Apache licensed alternatives or in some cases nothing at all was favorable. If Mac OS had continued to make use of GPL code and components that could have made a big difference to the whole software development community in a strategic sense. Instead this kind of zealotry resulted in barriers. Not only do you not have the control you imagine, but your ongoing efforts to draw these lines makes everything that much more difficult and unpleasant.
What this is about is the potential for naive copies where someone takes the codebase and tries to make essentially the exact same product with no significant changes. That would be a source of confusion and competition and not really serve anyone.
It is great to be enthusiastic about open source, but objecting to people sharing source code is rarely a good idea. I openly challenge anyone to make a functioning, useful fork of this project that would leave enough in place for this clause to apply.