You forgot the 'imho' at the end of that statement...![]()
I've been riding with a rucksack (originally a North Face on the MTB, now a Deuter Race EXP Air on the roadie) and I'm perfectly happy with it. It's even handier in Winter, as I get to pop a Creative Reflectives cover over it and attach another rear light to its LED loop!
Each to their own; rucksack, saddlebag, panniers or trailer - it's all a mattter of personal preference.
Everything on here is imho
I've ridden with a rucksack/backpack and with a saddlebag
With a rucksack the stuff you are carrying is at a higher centre of gravity. This messes up the bikes steering
Also if you are out of the saddle the weight has to be directly born down your legs and moved with the rest of your body weight which makes pedaling less effective
You can compensate for this but it is just more stress on your body and you are more likely to get neck ache and similar problems
The bike is a metal frame on wheels. It's job is to carry stuff about. So add a saddlebag and make it do it.
Backpack vs saddlebag isn't a matter of preference. Saddlebags are better in nearly all circumstances