Not true at all. I ride a dutch style 3 speed and I have a VERY hilly commute. My total climb is around 150 feet going to work and over 200 going home. The hills are mostly small but steep. One is around 2km long and accounts for nearly 200 feet of climb going home (it's fun going down though while going to work). My commute is around 8-9 km, so not that much less than yours. My city bike tips the scales at around 50lbs (just the bike), sometimes close to 100 depending on what I am carrying.

One can make a dutch style bike work nearly anywhere if they want to. Even fat, out of shape me has no problem with climbing hills on one.