Supposed benefits are that it is easier to render text on colored backgrounds (you can just render with alpha to a buffer and combine it with the background, with RGB subpixel rendering you have to consider the background while drawing), and you can scale text without color artifacts.
To be honest, we have plenty of computing power today, and our GPUs are underutilized most of the time anyway. I wonder why we can't just have RGB subpixel aware rendering of everything (not just text, but also lines and polygons) implemented as a kind of shader pass. Render everything at 3x horizontal resolution, and merge using an appropriate shader. And if you have a HiDPI screen, just drop the shader.
Though since DPIs are going up and 3 alpha channels is such an unusual thing, I guess they just figured it wasn't worth the trouble.
If there was a serious competitor in desktop they wouldn't dare to ignore their current user in pursue of new users.
There's nothing dealbreaking about the platform for me, well there's hardly even anything nagging about it.
Just fix fucking font rendering, I did use Windows machine as my workstation for 4 years, But I had to switch to Ubuntu, because of ridiculous font rendering they introduced in DirectWrite. I don't have money to pay for new monitor every 2 years, and I am quite happy with my dual monitor 27 inch 1080p until windows 10 changed font rendering to DirectWrite. It is fucking disaster in low dpi monitor. As always Microsoft ignored their current users in pursue of new users. I haven't seen this attitude from any other company. I haven't seen apple make font rendering on old MacBook worse to force people to switch to new MacBooks. Or I haven't seen something similar from Google. This is fucking total disaster. As someone who reads text for whole day (programmer) I care about my eyes and it fucking hurts my eye to see font rendering in new UI (UWP) and Edge.
p.s. Old/win32 application do use old rendering engine and are acceptable.