Some thoughts:
Colin Fletcher advised never tying anything on outside of pack because there it is more susceptible to abrasion and weather and loss.

Horace Kephart, a much better writer than Fletcher, but perhaps suffering from slight alcholic dementia and paranoia, said in 1906, to paraphrase, that keeping things inside a pack "kept them from prying eyes" or something a little crazy like that. It's had relevance to me on occassion, depending on plans.

Thirty-five years ago, my late mother, prior to her own alcholic dementia, knitted the only sweater she ever made, and gave it to me. I tied it on to my backpack, and lost it within a week.

There was a great photo on NF commercial Web site some years ago of Kitty Coulhoun or some famous mountaineer, with a small alpine pack festooned with tons and tons of crap tied on outside.

I own a couple of packs in 3,000 cubic inch range, and one that is supposedly 7,000.

It can be a hell of a nuisance to deal with the small packs on certain trips. Sometimes I deal with it and once in a while, I use the big guy...Am currently planning a luxury weekend trip in 30F weather, and wondering why I want to have any cares about packing --- bring the big guy and to heck with it, am thinking......though I could certainly take a small pack........

Rarely do I actually and absolutely need the big pack... It is by the way, a "Frostfire" Mountainsmith from about 1990--- relatively awful piece of s**t, but it works pretty good...........Still, I'd never, EVER look at another Mountainsmith pack ---- even though I assume current versions are totally unrelated..........

If you look around, you can probably get something similar for practically nothing. Most people most of the time, if they're into lightweight camping, are better off with the small packs, in my opinion