To repeat what I said in the other thread bat size was mentioned:
Definitely not true, don't know the magnitude of the effect but stiffness of cleft (which will increase with depth) clearly will have an effect on energy transmitted to a ball.
For me it's a collective conciousness thing, e.g. almost every top order player can routinely hit cover drives for 6 these days, hardly saw that at all even 5 years ago. Is that because of a huge improvement over 5ish years ago in batsmen or bats? Obviously not, just everyone now realises it's possible, so they try it, practice it and become able to hit those shots. The same with scoops and sweeps, in particular. Switch hits haven't got there yet, but give it time and they will.
Whereas bowling (in terms of pace/swing anyway) reached the limits of what is humanly possible a long time ago (noone these days bowls faster than Larwood/Trueman/Thompson etc or swings it better than Akram). This is an inevitable process, so maybe try improving the balls so that half the world doesn't use crap Kookaburras and improve pitches so that less cricket is played on easy paced featherbeds, rather than blaming bats for the recent progression in shotmaking.