200% is just rendering the same pixels and them drawing them 4 times and driving a single monitor at the single resolution is easy stuff. Would your HiDPI system with one monitor at 125%, one at 100% and another at 150% scaling? This is when the font rendering gets fucked up and your Hi-DPI native toolkits start blurring icons. That's my setup. Windows is perfectly capable to make this work. GTK wasn't able to do fractional scaling until recently and Qt has 100s of papercuts.
I got a Thinkpad to just run this setup under Linux 2020. AMD didn't solve the problem in their driver until 2022 when I was able to drive all of them at 60 Hz.
No, 200% is rendering 4 pixels with "features" 2x larger in each axis. You may get 200% scaling as you said with some legacy apps that give zero fucks about dpi scaling but are still scaled trough some mechanism to properly match other apps.
Fractional scaling has been a problem across all platforms, but I agree Linux has taken its time to get it right and still have some gotchas. You should try to avoid it in any platform honestly, you can get sometimes get blurry apps even in Windows. AFAIK KDE is the first to get it right in this complex situations where you mix multiple monitors with different fractional scaling ratios and have legacy apps to boot. GNOME has had experimental fractional scaling for a while but it's still hidden behind a flag.
It also helps to not have nVidia trash on your old (and sometimes even new) computers if you want longevity. My old machines have intel and AMD graphics with full support from current kernel and mesa.
I got a Thinkpad to just run this setup under Linux 2020. AMD didn't solve the problem in their driver until 2022 when I was able to drive all of them at 60 Hz.