lcds dont work great in not native resolution, even if its perfect 2x scaling it still little bit bury, so if you did that (set the displa to 1080) on the same display im not sure that's fair, at least that's what i noticed in my experimentation, and i had/have a dell, apple , huawei and asus laptops with hdpi.
for me the difference between high enough and 4k on a small laptop display is not that noticeable/important and it comes with drawbacks (at least on linux for now)
2x scaling is not setting 1080p, it's telling the software to draw at 2x scale. That's sharp and very well supported. True fractional scaling is not yet supported in most Linux software but I do 1.3x scaling for 1440p just by setting font scaling. Has worked fine for many years. Going to 4K from 1440p makes things easier on the software side as 2x is very well supported.
what i meant is setting the lcd display that has the native resolution at more then 1080 to 1080 resolution and comparing it to a native 1080 display would usually would not give the same results, as running the display at lower resolution (not scaling) would usually give you blur.
also fractional scaling works ok'ish in linux' but it's "fake" actually in that it uses xrandr to create a 2x resolution and show you scaling of that. and it uses more resources especialy with external monitors with different dpis.
No one ever runs displays non-natively to get any of the scaling being discussed here.
Fractional scaling works like that everywhere that I've seen. OSX does the same, and I'm not sure about Windows. The alternative would be properly scalable GUI toolkits which then creates other difficulties in mixed-DPI situations. I don't use that though. Font scaling is more than enough to get 1.3x scaling. Has been for years, and doesn't take the efficiency hit. It doesn't solve the mixed-DPI situation either though.
I am comparing with all other displays at about 150dpi (1080 on 14 in). Non-bitmap fonts are either jagged or blurry if you use hacks like hinting and subpixel antialiasing.
that is true. but there is a point about diminishing returns.
where at small enough laptop screen the increase in resolution gives you only small improvements, and at least still it gives you some downsides besides battery life.
