If well made and designed a carbon frame (considering it's monocoque), would be way stronger than an aluminium frame(no welds)...the only negative fact with carbon is that it will break without any sign of fatigue. An aluminium will crack before it snaps, not the carbon one. Also the ratio strenght/weight betwen carbon and aluminium is alot different...it allow you to get a stiffer frame with less weight of carbon than one made with aluminium because you can choose the orientation of the carbon fiber. Anyway haha i think you got my point!
What you dont consider is the wall thickness on the side of this tube where the aluminium part of the shock mount is "glued"...i dont know if you follow me haha! so what would be logical is that the carbon is thicker where the aluminium part is pushing and thinner there you dont need strenght.