Loading up powertop on my i7 6600u reports an idle draw of 5.5w with my browser open playing music. I think that's pretty damn good, for an old-ish laptop with mitigations enabled on Linux.
That assumes the motherboard vendor implemented ACPI properly, and most don't, you're often lucky to have something that is able to keep Windows alive enough to pass certifications. Linux, xBSD or macOS compatibility? Forget it unless you're talking servers with support contracts making it actually worth the effort for manufacturers.
Bottom line, linux on laptops only really works because of ACPI, if you were wondering what the laptop space looks like without it, I might suggest grabbing a couple random arm laptops/chromebooks and giving them a spin.
Right now I am listening to music on this computer while I work on another computer. When the screen turns off on this computer the headphones get switched to headset (telecommunications) mode and the music quality goes down... On a desktop computer where saving power is not a big issue and I certainly don't want worse audio just because the screen powered off.
It's been a long term issue that USB devices will not work properly if USB power management is enabled and that's scary when some of those devices are mass storage devices that could corrupt data.
As a single vendor, I trust Apple better to get things like this right, but I don't particularly like MacOS.
I think you'd have a pretty hard time finding an x86 system that couldnt run Linux these days. If you gave me a random x86 machine from the past decade, I'd actually feel more confident installing Linux than Windows.
FWIW the alternative these days is probably running a 32-bit RTOS on your battery hardware which isn't much simpler.