I agree that the larger cutting path isn't necessary, and I also agree that a 1" or 1 1/4" broadhead will get the job done just as well. That being said, I don't see how punching a 1 3/8" to 1 3/4" hole through an animal's vitals wouldn't do more damage and make it bleed out faster. Granted, a 2" cut is only available in a 2 blade BH, but there are 1 3/4" cut 3 bladed heads out there. The question there, in my opinion, is that too much resistance to get a good pass through.
Bigger may not be better, but bigger will absolutely get the job done faster.