That's about right for prep on a concrete sidewalk. The surprise is that they tamped it. Most guys I know just use 2"-4" of pea gravel and just pour on top after raked out.
The real question is how strong is the concrete they are using. If they are using fiber reinforcement, then the thing should stay true and strong.
Mt. Pleasant Eh? I grew up across the river in IL. Dated a girl from Mt. Pleasant for a while back in the day.