Except that if you are departing from CDG, you already need to know you are departing from Terminal 3 even before you get your gate assignment. At that point the separation of landside/airside concept is a benefit:you simply go to Terminal 3 because that's where you check in. And it doesn't matter if your flight departs from gate F14 or C89. Or if you get the gate assignment after you check in.

Conversely you will arrive in Terminal 6 for your flight and will not be surprised to see a gate 572 on your departure, pehaps going to Terminal 5 (because it's "logical") and being confused why you can't check in there. Instead you proceed to Terminal 6 and then to gates C. Also of note current T2B/D, future T4 which is causing also nowadays confusion, instead you have T4 common landside area and then you go to gates G or H depending on whether you are intra-Schengen or not. And you are guaranteed that the pax are in the correct concourse, and not hoping they are not on the wrong side because gates 401-422 are Schengen and 451-472 non-Schengen and how to explain if the gate is not assigned yet to the checking in passenger on where to go. (Not to mention the benefit if ADP finally decides to join the 21st century and converts one or two of the satellites to three-level S/NS combined operations)

Also you can't possibly mean seriously the suggestion that having lettered concourses is too confusing, but chucking terminals 7, 8 and 9 into one hall would not be.