There were many epic battles in market garden, but I think we'd all agree the most famous and epic was Frost's defence of Arnhem bridge. Historically, Frost was able to march down south along the Rhine and grab the northern end of the bridge before the Germans could react, although he wasn't able to get the south side.
In the GC you can't do this, because the Germans start with a good SS unit one move away from the bridge. In an MP game any opponent is just gonna move that unit straight to the bridge, blocking Frost and pretty much ending the chance for an epic recreation of the crux of the campaign right there. This is not even considering you have to take the time to attempt a grab of the other bridge west of Arnhem (Frost of course historically sent a group of guys to grab it whilst he continued his march to Arnhem, but the bridge was blown up in their faces).
Frost should be able to grab the bridge unmolested, so that SS unit should be a few more maps away, or something, and have to counterattack like they did historically. I'm not saying the GC should go exactly like it did historically, but this is a pretty damn important part of the campaign