Personally I can't confirm this. I've recently replaced the battery on my 2014 Thinkpad, and on low brightness I get around 8h of battery. That is of course, while not doing a lot of compute (compiling).
I don't think this was much higher, back when I used Windows all those years ago, so I'm not sure what people are saying with low battery with Linux? I don't see how Windows could get me much more? And why would it?