A tangible difference between the carbon and aluminium frame builds is likely the typical geometry they offer rather than their stiffness.
Carbon frames are generally longer in reach and front-centre distance. Look T20 of size M has a 427mm reach and Dolan DF4 sz 55 -- 414mm. Some exceptions include Bridgestone and S1Neo that are really short.
Very few alloy frames resemble this new geometry, for example Ribble Eliminator AL sz M and Ridley Arena Alloy sz M have a reach of 419 and 412 mm, respectively.
Both longer reach and longer front wheelbase is a trend. It would look very strange indeed to mount Glaetzer on Huebner's short and ugly Texima.