They can't go twice as far if the ride is up a defined climb. One you do the distance, that's it, you reached the pass, you can now only coast back down to the base.
In my experience, those on e-bikes are older and less fit in general, so it's not a matter of them making up for the work in volume; it's more that they couldn't do the climb at all without the assistance.
Also, your assumption about them providing half the work is surely wrong. Even basic ebikes provide 250W; some models provide double or triple that still. The rider provides probably 125W at most, so a third or less of the total power.
In my experience, those on e-bikes are older and less fit in general, so it's not a matter of them making up for the work in volume; it's more that they couldn't do the climb at all without the assistance.
Also, your assumption about them providing half the work is surely wrong. Even basic ebikes provide 250W; some models provide double or triple that still. The rider provides probably 125W at most, so a third or less of the total power.