A picture says a thousand words.
We have all seen this photo
So,
Has the ball size been significantly changed since the 70's?
Has the ball shape been significantly changed since the 70'?
Has the ball weight been significantly changed since the 70?
The answer is, NO! NO! and NO!, conclusively.
What HAS been changed though?
Field restrictions
Bouncer per over restrictions
Free hit rule
Shorter boundaries
Do any of these implementations create a bias in favor of the batsman?
The answer is, YES! YES! YES! and YES!
Now comes the bat size.
Luckily we have Barry Richards' bat saved in its original shape as posted above.
And as the ICC is looking into putting a clamp on tree trunks (and hopefully not a mild slap on the wrist), I would encourage ICC to implement a bat restriction rule where no bat should be bigger in size by any dimension than the Barry Richards' bat.
IMO, This will not only bring some much needed balance between ball n the bat but also separate boys from men, and save from yawning at sixes.