Dual monitor setup is a huge problem with linux distros. I haven't found yet any DE that works out of the box. I'm really looking forward to KDE with official stable wayland support, until then 2021 is not the year of linux desktop
But I think there is a general problem with sleep modes as mentioned. Luckily it boots in a fraction of the time Windows took.
Why would anyone not prefer this over a mixed set up? The only reason I see to use a mixed set up is if you're forced to use a laptop. Personally I don't optimize for working in meetings and planes though and my life is just simple and straightforward. I keep just 1 cheapo laptop around for that stuff.
With that said, XFCE handles mixed DPI/scaling just fine for me.