No idea either. That's an even more trivial source of damage than bombardment, and it just slows down your clear speed as you lose a third of your 'sprinting' time between packs. The only way it's practical is if you can guarantee you are blocking all the time while using the horse, in which case Akarat's Awakening would reduce the cooldown to nothing. What happens if you end up needing to backtrack through a cleared area though? No thanks.
In other news, Invoker 6pc is apparently wildly inconsistent in what is allowed to increase the damage it deals.
Invoker Interactions : Diablo3Crusaders
TL;DR --
Phys % on items = NO.
CoE in cube = YES.
Furnace in cube = NO.
Bane of the Stricken = YES.
Vo'Toyias' Spiker + Provoke = NO.
AE Damage on items = NO.
Hack = Unknown.
Bane of the Powerful = Unknown. (It's possible that the base effect works but the +15% elite dmg at Rank 25 does nothing for 6pc.)
Take with grain of salt since a lot of that was PTR testing, but since some of the testing was done in S5 and results are still inconsistent I'd say it's likely that nothing changed. Also remember that 6pc is by far the largest source of damage but it's not the ONLY source.
My suggestions would be:
Reroll AR on Justice Lantern to CDR.
Drop Amythysts for Rubies in legs, reroll Smite% to Armor.
Reroll Move Speed on boots to VIT. You lose 130 STR (after Finery) in your Paragon, and gain up to 650 VIT.
Reroll crit on bracers to either LPH or Phys%.
If sheet CDR is still under 50%, maybe consider switching gloves from IAS to CDR. If it's super close, you could squeeze out 2% more CDR on shoulders too.