RollCNY: I think I might know the answer to your question, I was reading a training guide and apparently ( in theory ) not sure it has been tested, Your legs are conditioned to the kind of position you ride. So technically ur legs are conditioned to perform in an upright position and you pedal more efficiently compared to that in a dropped. However, you can swap over but at first you will notice a perform deficiency. Same goes for any swap between aero,drops and flats.I assumed you have recently just swapped bikes.
For the rest of you, I created this article because I was really interested between the too. I've been riding flat bar since I was 3 and have thought of buying a road bike but the drop bars are iffy to me and was really interested in the difference. I guess you kind of get use to it after a long time. Plus I believe what is said above has to do with the feel of each rider.
I got my own theory about the climbing up hills part. I had to lower the stem myself as I found it too high and I wanted to be more aero dynamic as a cheaper alternative, when I stood up and sprinted. I got the same feeling on my friends road bike, like I was grounded to the ground. I assume have your weight on the handle bars due to forcing ur back to straighten out causes the wheel not to lift of the ground. I believe the height between the stem and headset has to do something with the feel too. Not sure, just a wacky theory.