The "wheel" is 40 years old. It's a great wheel, it's doing a hell of a job. But with 40 years of perspective, maybe it actually can be re-invented better without carrying around a pile of legacy back-compatibility needs.
Neither of these things has any bearing on the quality of Linux, or lack thereof.
Also their goal is not to run 100% of POSIX or Linux specific software, rather achieve a good enough compatibility to run majority of well known projects and utilities.
Newer is rarely better. Besides, in computing, so many "new" things are just rehashes of old (and not so old) ideas.
I really wish we could get away from the "that software is old" meme in this industry.
New software, otoh, hasn't been through a 40-year shakedown cruise.