Lets be clear- a cut swing is not swinging straight down, its more so just a more flatter swing that a traditional baseball swing which is a slight uppercut.

If all you're trying to do is hit homeruns, traditional is probably better. However, most ppl have to deal with HR limits so we don't have the luxury of hitting 2 HRs in a game. If you want to get all scientific with it, statistically speaking you're more like to get on base if you hit liners or hard grounders https://library.fangraphs.com/pitching/batted-ball/ , which is the point of a cut swing IMO. If you're at bat with no more HRs to hit, it's better to take your chances can try to hit the ball hard on the ground than try to lift it and risk the HR.

Not everyone should do a cut swing and a cut swing is not for every situation, but clearly if the pros do it (along with the overlap) theres something to it.