Ah now that opens a whole new debate
OK for hills I generally go up at a speed I would when doing longer rides in a sportive etc. I did at the start take it easy as you suggested but these are not mountains but maybe 100-200M at a time. Therefore if you ‘rest’ on the down hill and flat any glycogen you use on the climbs (can be longer ones of 1-5km) you will as you say replenish anyway.
We should remember of course the important factor of cadence when climbing and using higher cadence vs slower one because that’s aerobic vs muscles strength and one of these uses up more glycogen.
I was listening to a fascinating podcast with Mark Sissons and Jacques Devore which I would recommend anyone listening to. This was about cycling but can apply to any endurance sport (and in fact this whole topic is) and he used to train (Jacques) the US pro David Zabrinsiski.
Now he did dope but he also made a boig change under the guidance from vegan carb burner to primal fat burning (Primal is Keto but only now Mark is admitting it !!) and his performance both climbing and TT went up and what they said was his aerobic system was the key.
So for those of us doing this fat burning allows much more aerobic performance if you get the cadence up, lower cadence will use more glycogen and for me I think 80-90% of cyclists are now fat burners and certainly most marathon runners are. It is just for sponsorship and other reasons most will not admit it.