It is quite a bit worse in practice depending on what you do.
For example, with web browsers, most Linux ones (including Chrome and Firefox) disable much of hardware accelerated graphics on Linux by default because of "unstable graphics drivers". If I remember correctly, Chrome just disables it across the board, while Firefox has a whitelist of drivers considered stable which is basically just Intel.
In my testing, unless you muck around with these settings, you're can easily lose something like an hour of battery life compared to Windows if all you do is just browse websites (and I'm not even talking about anything fancy here; my automated test was literally just scrolling the main Reddit feed).
I think its just a battery life issue, and as far as I know its not much worse than windows.
If you are going to carry the power brick around with you anyway, might as well just plug in it a little earlier.