My Barrett Fieldcraft 6.5 Creed has an 18" barrel.......deer don't mind being killed by it! Do I have to adjust my dope for that rifle ...yep. But figuring that out (at the range of course) is part of the fun. I limit myself to shorter shots because of the energy loss at extended ranges, but that rifle is for a specific purpose. If I plan on longer shots (500 plus) I take my 300 WM. The point is if I was a "One Gun" kinda guy then yes a longer barrel would be better suited for ALL the hunting/shots I may encounter. However, If I were a One Gun guy my rifle would not likely be a 6.5 Creed either.
When I ask myself what length barrel do I want in a new build, my first question is what do I have already, Then what environment will I be carrying it (mountains, plains etc) and the farthest likely shot. Its always a compromise but what I have learned over the years:
1:You carry the rifle way more than you shoot it so weight may be a bigger factor than some realize.
2: barrel length is not always synonymous with weight. I tend to go thinner profile and longer length and that works. If I go short then I tend to go really short...so the advantage goes the way of portability.
3: In the end I build what I want and justify it however I need to....then I build in the opposite direction as well!