1st idea
has already been said, simple increase the procs with each feat point spent on it alongside the damage
2nd idea
remove the damage that each feat point gives and replace it by procs to, for example, 6-8-10-12-14, AND the damage increases with the reaver stacks, much like the overpower ability (sadly this ability only has the name to go for it much like the sever
)
3rd idea
add a different proc to the off-hand weapon, meaning that a barb can have 6procs to the main-hand weapon and 6procs to the off-hand weapon, giving a total of 12procs to dual-wielded, but only 6procs for 2handed weapon
4th idea
instead of changing anything in the tree, wait for the new perks that will come out in far far way and distance future, that will increase lower tree abilities stuff (for all classes), making revamping classes unnecessary and avoiding overpower issues at lower lvls between classes