Pease read my post # 45 again. In second paragraph I mentioned custom build boats have great engineering. You are taking comparison between custom and production builds in the wrong light - IMHO. Read all the other posts too.
Actually what you said was "Some custom boats experience great engineering." Bad to be misquoted. Worse to be misquoted by yourself.
That distinction is extremely important as they can have horrible engineering. See, "Northern Marine" and "Baden". That's a custom boat. See a new megayacht built by a large builder that then took two years at Rybovich being made acceptable after delivery.
The fact is that most of us don't require a custom boat as there is a production or semi-production/semi-custom that meets our needs.
We have built a semi-custom boat while others were pressuring us to go with a custom builder. But the benefit was we got a tried and true hull design and we got engines and equipment that had been used in identical boats many times. On the other hand we had a lot of flexibility above deck and some in the staterooms as well. Still, we made very few changes from their normal builds. Sometimes time and experience really lead to a good product. I've looked at the Bayliners and just wondered how else would I arrange the living areas, concluding I think they did a great job. Sometimes it just works.