The Customizer is an absolute hash-up with few themes -even from the same developer- having exactly the same layout.
Customization is something that should be in the theme, not the core. Suffusion was an excellent example of a well thought out customizable theme but Mullenweg and cohorts kicked it out because it didn't mesh with their idea of customization.
Gutenberg is yet another thing being foisted upon an "unwanting" world. By all means offer it as an option but there are already excellent page builders out there which do the job even better.

Perhaps WP should consider two branches - the one that everyone can use in everyday work (next stop WP 4.10.0...) and "bleeding-edge" (5.0 or even 7.0).

As for all you developers sitting on the edge of your chairs waiting for 5.0 to go live; surely the most important thing is security. You already have your base and are working with it. Why the urgency for 5.0. As any old lag will tell you, you should never install a .0 version anyway - remember Windows 3.0, remember Novell 4.0 and 5.0 just to name a couple?