It would be like having a back pack on one shoulder vs. both...although the strap on your chest helps distribute the weight.
Not that it's horrible, but it's not for me. I also find that I never use the "sling around" option, probably because my lenses involve a fuss to change.
For just 2 lenses + cam with lens + accessories, it's more than enough room.
Mine has: K10 + grip with 24-50 attached, 90mm in the main pocket, and filter pouch in the little slit (and step up rings and rubber lens hood)...
Top has 80-320 + charger cord + little stuff like pen, paper, reader, etc.
Front pocket: battery, rechargeable batteries, memory card case.
Bottom: flash + wireless trigger/receiver, Zenitar, camera battery charger + cord, regular battery charger.
There's still room in the top for a multi-tool and some flash drives
