I had to laugh about the advice for a compact crank. There are no hills in the Detroit area, unless you count riding up and down parking ramps. I once did the Wolverine 200 on Belle Isle, which had something like 1 foot per mile of elevation change.
Maybe, but if you ever venture out of the metro area thing could be different.
We did a 900 mile loop around the Lower Peninsula last summer with a total elevation gain of 30,000 feet. No big hills, but a lot of little rollers. We were on loaded touring bikes, and I did use my low gears at times. North of Rose City the topography got a lot more interesting.
I don't know about the OP, but I've always ridden road bikes (the last 50 years). I didn't like my X-mountain bikes because of their upright riding position. It puts too much weight on the bottom.