Fleet actually makes your random charges better, but I guess you consider it a nerf when everyone gets the same threat range instead of specific armies.
The fleet is a nerf
12+d6 is higher on average than 6+rerollable2d6
It's also a relative nerf. The average threat range of fleet units went down while their maximum remained the same. For non fleet units, their average range increased slightly while their maximum range increased massively.
1,000 witch hunters (trying to get rid of this)
1,000 SM (trying to get rid of this)
680 Tau (newest addition)