While that might be true for a certain group of frames from a certain time period, again, it's a generalization that isn't true by nature of being one material or the other.

There are many different alloys of steel and aluminum. And then further multiply those by various processing (annealing and heat treating) that can change the mechanical properties of the alloy, making them more ductile or harder or stronger. And then further multiply that by the various grain structures that can be produced with modern alloy production techniques that give the metal different responses to different types of stresses, impacts, and strains. This scientific paper demonstrates how variable a metal's response to force can be depending on the type of alloy, tempering, grain structure, and direction/type of force.

To put it shortly, a material's properties are not set in stone, so to speak. The way modern aluminum responds to stress can be made very similar to steel, depending on how it's made and treated. We already see this with the way steel production has evolved over the last four decades. Frame makers in the 60s would never have even imagined the steel alloys that exist today with corrosion resistance and UTS in the 2000 mpa range. Same for aluminum. It makes no sense to say "aluminum" acts a certain way in general. Too many bicycle enthusiasts have tunnel vision when it comes to modern metallurgy and production.