The simplest description of electrical assist is that it flattens hills and knocks out headwinds.
I enjoy riding a lower levels of assist but bump this up a notch or two when I encounter a grade. My pedal rate and pressure remain unchanged. The hill disappears.
Strangely I learned to enjoy attacking hills on a fixed gear bike. I could stand and apply high torque without wearing myself out or risking blowing out my knees. The thick chain and stiff frame of my fixie directed all of this force forward. Very satisfying but the exact opposite of riding with assist.
The assist on a climb can make you feel weak on the downhill side. Say you are riding with stronger riders and using assist to climb with them. On the downhill they will take off and quickly exceed your assist speed limit. Now you are left on your own to try to keep up with all of the bike's Inefficiencies.
The Bosch motor isn't particularly strong so steep hills present a problem. There is no granny-gear so you will have to attack steep hills with torque that the assist won't match. Plus, friction from the nylon gearing in the drive increases quickly at higher torque. Assist Modes have little effect since all will be driven to max assist.