With tlp and a 5.10ish kernel, my T480 handles light web browsing at 3-5 W depending on display brightness (wqhd display). Heavier websites, high-res video decoding, etc. will bring it up to 7-10 W. Maybe 20 W when compiling something, or when attempting to use the (worthless) Nvidia GPU (which I leave powered down most of the time).
It has a dual battery setup with a 24 Wh internal battery and a 72 Wh external battery (I use the bulbous 6-cell, but you can get a thinner one if you prefer), so even when setting the charge stop thresholds at 80% to preserve cell lifetime, the computer easily lasts all day on battery.
That being said, it would be easy to find a random laptop that either idles at something stupid or that can't go to sleep properly because of just one wacky peripheral, making Linux power management seem bad.
Half the battle is picking the right starting point (e.g. a Thinkpad), and then setting everything up so you can actually measure the power in all of the different states so that you can actually confirm that your setup works properly before relying on it and ending up disappointed at the airport.