OK, I agree with majority that FH slice is a niche shot and your basic rally ball and aggressive shot should be a topspin FH. This is high percentage tennis and is the goal.
But, there are always exceptions. I have played against and with a guy who won at 4.5 level with 90% of the FH being hit with slice. He did play mostly doubles. He also won 4.0 singles matches and won more than he lost when he was in his late 50s.
Don't forget Paul Annacone was in the top 20 (maybe 10?) and he hit a touch on slice on most of his FH. I saw him play McEnroe in an exhibition and he stood in and attacked everything with underspin off both sides. I would venture that Annacone would beat all the 5.0s on this board playing nothing but FH slice if he wanted too. McEnroe was another great example as he hit a high percentage of FH slice and could kill 5.0s and down.