Really? The 70-200 is a standard wedding lens and the IQ of the 70-300L is very,very close, especially at the short end
Perhaps you had forgotten that between 70mm and 200mm is 85mm - which is the 'standard' portrait length?
Also in weddings shallow DOF is NOT wanted for most of the shots as it is a sure way of getting shots with the further eye OOF
Since I have the 70-300L I know about it's good iq. But sadly you have forgotten about two things: 1. He's using a crop camera, so the wider and is 112mm to begin with.
2. dlsrs autofocus with open aperture. You should learn about these things, just buying expensive gear is different from knowing it! There are many forum posts for the details, or use an internet search engine like Google. It doesn't matter that much with the 7d/5d2 as with a 5d3 af system, but all the same most capable photogs will tell you that af'ing at f4 rather than f2.8 in lower light results in less keepers, even if you *shoot* at smaller dof for safety.