If you're going to be shooting clays, pheasants, waterfowl, or anything where you're following the target with a smooth swing then I'd agree that longer barrels are a plus. However, you mentioned hunting grouse and woodcock in the UP so I'm going to disagree.
I live in the middle of the UP and have been hunting here for over 45 years. In my experience the key for hunting those birds is quickness. They both flush explosively and the window of opportunity is very short. You're mostly snap shooting by instinct with little or no chance to track the bird in flight.
That gives a big advantage to the short and light gun over long and heavy. I've had a lot of success with 26" barrels on doubles and singles but recently switched to 22" and am liking it. I'm even looking over the choices in 20" coach guns since they might be even better for where I hunt.
You're likely to find that the ideal multi-purpose gun doesn't exist, and if you want to do everything you'll end up with more than one gun.