I forget the numbers, but I had a long round trip drive where I had a 4000 foot elevation change. By the end I had an impressive electric range on the trip computer. Coming down on nothing but regen I picked up 5 miles.What goes up must come down......at least electrified powertrains can recapture a good amount of the energy on the other side of the hill. I'd bet there is less dropoff than in a pure ICE. ICE's are least efficient (excluding diesels) at low load/low speed and under frequently changing power demands, which they often are operating in when going slow in low range. Electric motor efficiency is pretty static under all conditions.
Of course, it was at the expense of all that gas to build up the potential energy.
TFL overlooked the same thing they did on a 4xe video. The engine came on just before they reached the summit. They stopped the video there and didn't say anything about the drive back down.