Of course, it's important to be able to slice with your topspin grip.
But think, WHEN do you use slice? Usually when pressed wide on a full speed run, so you need to be able to take the ball late, or behind you, like the pros. That is the basis for conti with a slight twist towards eForehand.
If you can take a ball with your normal forward contact point, why bother to slice? Especially a slice that is fast with moderate spin? You slice to get heavy backspin, hopefully to cause a skidding ball, and with offspeed and skidded bounce.