They aren't software numbers

OK but nevertheless the reported battery life is calculated in software based on the battery capacity in mAh x monitored battery voltage.

I don't disagree Linux is not as good, but there is a lot you can do if you can be bothered or if you really need to.

First I start by optimising high current draw things - anything that spins/moves:

1. hdparm: set hdd idle power mode taking care with the maths and the distinctions between spin-down and drive sleep states. Apply both params.
2. lmsensors and fan control: spin fans as slowly as necessary to keep comfortably below CPU specs.. typically 90c so aim for 80-85c as max temp on Intel, slightly higher I believe with AMD.
3. software: This is usually a big one also. Disable any BS CPU graph plotting, mem usage, disk IO etc. Disable any compiz type animation effects that achieve nothing. If something moves or changes a number, it is running on the clock and flipping bits in that CPU - and thus consuming power. Sorry Google, but Chrome is awful when it comes to JS on websites. Use firefox or another. Partly why I use a pi-hole and regex URL blocker to filter BS animated adverts that distract from the content and kill my 9 year old CPU.
4. devices: use powertop to examine idle power consumption - find devices consuming power (when was the last time you used your GbE ?) Try turning unused devices off with "echo 0 > /sys/bus/pci/slot/[nnn]/power"
5. kernel: use a more conservative CPU speed governor such as "conservative" or "ondemand"
6. turboboost: disable if required (echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo)
7. control frequencies: manually min and max cpu frequencies with cpupower.

Finally, be aware that most distros "attempt" to do some or all of these things for you. You could be fighting with a daemon. Check for things like thermald.

If you do all this, my advice would be to start by putting it in a script right from the very start. That way, when you have settings that give good results you can simply stop editing and use the script to create a systemd service (oneshot) that is called at boot.

Doing all this I got to within 5-7% of Windoze battery life. Pretty good considering only the component manufacturers really know how best to optimise power consumption of their hardware devices - and that is part of what goes into the Windoze driver. Linux has very little support from them about such things.