I'd always seen terrible power efficiency on battery with Fedora. It was much worse than any previous Thinkpad. I mostly treat it like a luggable, always plugged into the wall. I wasn't sure if it was the CPU or chipset, but it never got into deeper package-level idle states like other machines.
However, I recently discovered that if I suspend and resume the laptop right after I switch from AC to battery power, the laptop runs in a much more efficient mode. It gets into those deeper idle states and can get almost 6 hours of life out of its aging batteries for basic office/communication tasks with wifi. If I don't suspend it once, it will only get close to 2.5 hours even if almost completely idle the whole time.
The Nouveau driver was so bad here that I blacklisted all the drivers and just use the Intel GPU. It's the difference between 3 hours or 6 hours of battery.
It apparently ran the Nvidia power on even when no program wanted to use it.
Are you sure you didn't install nvidia drivers? That is a common symptom with nvidia binary drivers. Nouveau on the other hand is fine with powering the device off when not used. For nvidia drivers, the bbswitch method is more reliable, but is apparently deprecated by distros these days.
Yup. By adding a Nvidia card (or, far less commonly, an ATI/AMD one) they can sell that laptop as a specialty "Gaming" machine - and with margins on commodity hardware being so razor-thin these days, that's exactly what shrewd marketers need!