Career resumes are similar, and I suspect Dennis has more WPA titles, but the thread is about who'd win an all-around today, and it's fine if you wish to call Alex a slight favorite, but this would be really close.
If and when Alex snaps of the all-around at the Derby, it will speak volumes. Each of them has won in all three primary disciplines at the Derby, but Dennis has also won the Big Foot 10-ball and also the DCC 14.1 event. I don't think Alex has won either of the last two. No other player in the world, to my knowledge, has won all five of these events at the Derby.
Actually, if anything, his snooker performances subtract from Alex's resume.