Materials make a difference. Thickness makes a difference.
Just because JBL and Altec used to use 3/4 inch ply, does not mean it was the best material. Testing methods, building methods, material availability, construction methods, etc, were nowhere near as advanced as they are today.
Speaker and cabinet technology has come a long way. Driver materials have improved (less resonance, better damping, less flex, lighter, more rigid, etc), speaker cabinets materials have improved (constrained layer damping, less resonant, better damped, composites, CNC construction for better shapes, etc, etc).
I can speak from direct experience. I have a friend that used to be a speaker designer and builder. I used to help him out. Several of his designs were bought be some pretty well known companies.
When he was designing a speaker, he would build it in a real basic box, just to get it close to sounding correct. Once he got to the point where is was very close, he would then build a box using CLD, with thicker materials and baffles, and the improvement (without any other changes) was not trivial.