It's more like how every athletics record gets broken every so often, or how they have to keep making Augusta harder to stop someone hitting a 60 at the Masters.
If you can measure it against a constant, it's getting better.
In cricket we only ever measure what is being done against other people, so it's staying the same.
Athletics is different now. You should look into the difference in track technology, shoe technology, hydration, diet and potential for performance enhancing drugs (you may already know) - the same in swimming the pool , the depth, water flow etc it makes a difference and what they wear. Same in cycling the bike technology is insane now (and drugs use)
In golf, the ball makes a massive difference let alone the club head shape, grooves, club head weight, shaft weight, shaft stiffness, grip thickness and feel, tees, caddy. Then there's the course and the lay out of it. I could go on.
If we want to compare cricket to these sports without a doubt it would be far easier to bat now for someone like Bradman. Take Tiger Woods back eras in golf it gets harder for him to play - everything is against him in terms of ball and club technology - not to mention the fact he would have less to play for financially and fame wise, less fans. The further back you take Smith the harder logically it gets for him - uncovered pitches, worse bat, worse gloves etc, worse umpires even. The further you bring an ATG player the easier it should get for him with the bat in my view, always. The further back you take a bowler the easier it should get. Just my thoughts logically. Sutcliffe I'd wager to average 70+ now despite the struggles currently, he was an ATG - this isn't a David Warner, Rory Burns or whoever - it's an ATG cricketer - he would be brutal to bowl to even on a green seamer in England considering he held a 60 plus average his entire career. It gets even harder if you look at Bradman (in my opinion)
The only factor with Bradman was whether or not the umpires were scared to give him out - he often he nicked off / plumb and wasn't given out could be brought into the equation here - and if he benefitted from very favourable umpiring I would be happy to massively adjust the estimated average for him. If he didn't well then..all just speculation , but my opinion anyway.