I’d say the bowlers on average would be slower. The physical standard was a lot lower in those days. There’s no accurate recordings of the speed of the bowers he would have faced, but he himself mentioned having faced speeds of 80-85mph. The footage I have seen of him playing certainly looks that on average he’d be facing weaker bowlers than those of today. Though the spinners of his era had wickets that were very much in the bowlers favour.
There’s pros and cons to his era, he played with less protective gear, worse wickets, worse bats, but played against less tactical fielding formations and didn’t have to play a wide variety of teams (Which is a double edged sword, as the batsmen of today will face a fair few weak teams, whereas Bradman predominantly played England). He also played a smaller amount of games compared to the players of today and his career was interrupted by WW2. If he played today (and in this hypothetical scenario had grown up and adapted to the current cricketing world) I imagine his average would be significantly less, but still impressive. It’s a frivolous estimation solely based on my meagre knowledge of Bradman, but I’d say he could average 70-75. I’m basing that on the fact that during his playing career, he posted averages that were basically double that of his peers, no one came close.