Are you on Zebbs (9.9)? By front heavy, do you mean the forks dive into their travel? With 1 or 2 tokens they do, they lack decent mid support. With 3 spacers in the fork you get decent mid support from the Zebbs, not quite Ohlins level, but very good and there was no discernible loss in compliance compared to 1 or 2 tokens in my opinion.
Ive driven the KSL and it is indeed lighter. For what its worth I have an Enduro, and switching between the Enduro and Slash+ is easy, compared to Switching between a Gen 3 Levo and Enduro where the weight difference was very noticeable.
I like how the battery doesn't come too close to the head tube/stem area on the slash+, its one of the reasons I bought it. it was one of my gripes with the Levo. It felt much heavier.