Linux is powering servers and high performance computing because it is good at these things: mostly static hardware configuration, set up once during system installation high performance, modularity and the ability to inspect a deeply running system of you are an expert. It ticks all the boxes for these specidic environments.
On the desktop, not so much. For example, the concept of device files is hindering use cases that should "just work". When I plug in USB headphones, a new audio device is created. Fine. But I need to enter the device file name or ALSA device string onto half a dozen programs to use it. All I would want is to have the audio rerouted automatically. Pulseaudio was touted as the solution to that problem, but ar what cost? We're now literally stacking audio systems on top of audio systems and sacrifice to arcane gods to have it work.
When I plug in a USB drive, I now have to look up its device file name in order to mount it manually. The software stack required to automount it from a desktop environment is atrociously complex, because it requires root privileges to mount a device not listed in /etc/fstab with a user flag. And because any number of drives can be connected in any possible order, no entries in fstab can be made.
This clash of UNIX-like concepts and modern user expectations is what is holding Linux back. The underpinnings are not bad. They were just designed for a different task.
So, yes, you can build a user friendly OS. Yes, it can have a clean design. But it won't be called Linux anymore.