I think what you're describing is a symptom of the issue. The issue is talent churn. Bright folks who start a feature get poached and leave and the feature dies on the vine. Or that the feature, which started off great in it's own little corner of the engine, was a mess to integrate with the rest of Unity due to it's architecture and the fear of breaking backward compatibility.

The problem now comes not from tech-previews but from the quarterly forced releases because it's now a subscription. The entire business model is flawed and outdated. Same with Unreal. The difference is Unreal tech is exponentially better than Unity architecturally and they know their audience very well so they were able to get in with virtual stage production, games, movies, you name it. They were successful in expanding beyond their core. Unity, can't. They don't know how.

It's a tough spot to be in. I knew my place when I shut mine down and open sourced it. I couldn't compete. For Unity, they have a loyal fanbase that wants them to succeed but I'm afraid it's going to take breaking everything they know in order to do it.