You both are right, and both are forgetting one thing that is unique to the O/U rifle, and that is the effect of one barrel being in line with the verticle, and horizontal axis of the rifle, and the other barrel being above that same axis! Each barrel reacts differently to garvity. What this means is the rifle recoils back, and up from the bottom barrel, just like the top barrel, but with far less muzzel rise, than the top barrel. This is something that is not a problem with a S/S, both barrels being at the same hight above the axis of horizontal, and verticle center of the rifle.

With the O/U this difference between the barrels, causes it's own set of problems, but only when regulateing, and it is true the change of bullet weight, in an O/U, is not as drastic a change to the regulation as it is with the S/S.

Suffice to say, they are too different animals, but both have their crosses to bear. There is no free lunch with either of them, both demand some knowledge, on the part of the owner, to be useful !

I have both, but I prefere the S/S, to the O/U, for hunting anything that bites back!