It was already shown that SteamOS is way better in terms of battery performance than Windows. So if Windows uses power saving mode by default, these results are even more damning:

There might be some tweaks to mitigate some of the short comings of Windows, but that doesn't changed that the script has flipped. Before it was Linux that required tweaking and Windows would have a decent out of the box experience. Now SteamOS works great out of the Box while Windows needs tweaks. And at that point there is no reason for sticking with Windows unless your software specifically demands it.