

What you say could be boiled down to:
If just everybody concentrated on making quality software for Windows, we could have much more quality software for Windows.
Your view is common but irrational.
The concept is described by Linus Torvalds as “Scratch your own itch”. The richness and diversity of Linux distros is a strength not a weakness.
If you want to make a Barbie themed distro you can. And if you want to, why should anyone try to prevent you?
If development was concentrated around fewer distros, it is far from a sure thing this development would go in the direction you would personally want. You would just have fewer options.
Progress is always welcome, congrats to them for finally taking a step in the right direction in this regard.