Actually a bigger example is the entire Italian Campaign; basically a waste. Easily defensible terrain that tied down only a tiny force of Germans.
Theater definitely should have been shut down after Italy surrendered, and a case can be made that the Italian mainland shouldn't have been invaded in the first place.
I also strongly believe France should have been invaded in 1943 but that's a a pretty controversial one.....
Just before this you state the reason why we didn't land a year earlier. Because after the debacle at Anzio, the American military command was scared crapless that such a tiny force of nazis with insufficient air could kill so many Americans. Yes we won Anzio, but it was bloodbath for our boys and it shocked us how few nazi's there were there after they surrendered. I feel it was at this point our military changed to a "blow the hill to the gorund and then go see if anyone was defending it type strategy". In the western theatre at least.