One of the problems here is that power-draining can happen by different components. Quite popular are graphics chips, but other components can be part too. For example, a friend of mine has problems with his device waking up from s2idle during transport. That is not exactly what you would expect in such a discussion, but from a users perspective, he has less time to work with his device given his usage pattern.
For me, this isn't much of a problem as I prefer working on a desktop, but I wouldn't accuse someone of being a liar just because he had a bad experience with power consumption on Linux.
acpi patched_dsdt.aml
This has the advantage of not requiring any manual intervention every time your kernel is updated. The downside is that if you try to dual boot W10, it will BSOD on boot with an ACPI error. To overcome this, take the original dsdt.aml and load it in a custom (not auto-probed) menu entry for windows. You can just clone the auto-probed line, and add before the chainloader line:
acpi old_dsdt.aml
Sadly, the 6th edition of the Carbon also runs waaay hotter than the 3rd, and I did notice occasional coil whine which was previously absent. When running normally the kernel writes regularly about thermal warnings. It seems that power and heat management is not well managed in this edition, and I see similar reports for the x1 yoga 3rd gen.
My system is exceptionally lean. I run bspwm and the radios are always off except WiFi. Still, I feel like I could get a lot more from this laptop. I cannot (and I certainly wouldn't want to) install Windows on dual boot to make a comparison though.
What distribution do you use?
I personally use debian unstable with a tiling window manager (awesomewm) without a specific DE. However, I generally setup Mint for all my colleagues on the same laptop lines, and there's one colleague running Arch. We all have very similar battery lifetimes.
High-end laptop lines (Dell, HP, Lenovo) have actually pretty good linux support, they are almost always intel i5+ cpus with integrated graphics which are all very similar. There is next to zero setup required in almost any case. This is known. The drivers are tried and tested. I've never experienced any random "power management issue". Suspend/resume/battery consumption/acpi is working perfectly fine. What else does qualify for "power managment"??
I've been supporting a team of 20+ people with these lines in a mixed environment, and linux since more than a decade was always basically plug and play.
There have been some quirks in some models, which generally required some tweaks in the kernel boot line, to fix issues with backlight tweaking.
Sure, but Linux really ought to shine on the low-end laptops.
But this doesn't save you from crappy hardware, which is why this kind of argument is a non-starter for me. How well does current windows editions work on low-end crappy laptops that sell for the lowest tier? Not great. These laptops have plenty of little issues on windows as well.
Maybe better than linux, because the drivers have way more work-arounds than linux has.
Have you ever seen the internal linux quirks table to work around buggy and downright horrid hardware? That's what you get with those. If it works at all is thanks to the patience of people that put in the time to work those issues around. I frankly do not blame linux if it doesn't work well with such hardware.
On my current X1 Yoga 1st gen, I do regularly get almost 1.5x the uptime on battery compared to windows 10.
We got a batch of X1 Carbon 6th gen, which are "optimized for windows 10", where the S3 sleep state was replaced by the S0I3, which is OS-assisted. The X1 Yoga with S3 can both suspend and resume faster than windows 10, despite not having S0I3 (and has longer battery lifetime to booth).
And by fast I mean that by the time the lid is up, the OS is ready. By contrast, windows 10 seems to always shuffle for several seconds after resume, even on the carbon 6th gen.
So please...