Heavier packs have beefier suspension but that is a bunch of BS when you do hike. Because it's not only your upper body that gets strained but also your legs and knees. When you have a heavier load your lower body will feel the gravity pull of the heavier pack much more than a lighter one and they will feel tired much faster.

But Does that mean heavier packs don't have their place? Packs such as the Bora are made for Sherpa dads who will need to carry tons of load or for expeditions since they need much heavier and bulkier equipment, so they do merit their place. As for us, we are mostly hikers and lighter packs is the way to go for us. As most mentioned here ULA, Granite Gear make excellent light packs. I would also take a look at the budget level REI Cruise UL pack. It weighs a bit over 3lbs but is excellent at transferring weight.