Unless of course that is what your trip requires. I'd hate to ride a 450 from here (southern NM) to Moab, then explore canyonlands for a few days, then back. My 640 excels at that. However, if I was riding to Canada and Alaska, even if I was doing 1000 miles on the Dempster, 200 on north Canol, 150 on Cantung, a couple hundred on the Joseph Campbell (all dirt roads), even the 640 would be ill adapted, and I'd probably take my GS. Of course none of those are ideal for local desert riding, where a 450 would kick ***.
I could ride mostly dirt from here to Moab, but sometimes that just not in the cards due to time or other considerations.