I thought similar to the OP in the past, and because of that, I have the Priority Onyx with Nuvinci CVT (their N330) and another bike with a Nexus 8. In my opinion, the Nexus is much less efficient. The Onyx with the Nuvinci is a bit less efficient, but not significantly. The Nuvinci is really nice while riding up a hill as you can dial the ratio as needed to keep up with slight increases or decreases in slope . . . and, for me, all done while mashing the pedals as I'm up and out of the saddle under a load!
I also have a couple of 1X's (which solves half of the derailleur problem
) and for myself, I can't imagine NEEDING much more than 330% or so of gear range (and I ride some very steep hills too).