Honestly, that should be the case, regardless of the camera body. With a lens bigger than a small prime, you should be holding it by cradling the lens with your left hand so your right hand is free to work the controls.
Yes, you are right. We all cradle the lens with the left hand. Duh. But the difference is that with the SL-1 and a large lens, you might not be holding the camera at all - just hitting the buttons as needed. It's a little weird when you start putting longer lenses on it - even ones as short as the non-L version of the 70-300 IS.
Yes, I actually hold the 5D III camera itself no matter what lens I am using!