Swap out the speed for more Crit Damage/Def/Atk. You can run Fellhound at a much much slower speed if you're only planning to use him as a Campaign farmer. If the AI estimates that it can kill the wave it will never use A2 and A3. Masteries are also important. 

For reference: This is Chofly's guide on this with the minimum stats needed for consistent 5 second runs- The FASTEST Campaign Farmer! | RAID Shadow Legends - YouTube 

mine has a total of 109 speed, just need enough to go first in each wave.  Crit rate needs to be 100, defense as high as possible, attack as high as possible, and crit damage wherever you can get it.

no other stats really matter, so you can get rid of all of the speed gear.  use crit rate gloves, defense% chest peice, defense% boots, you need 1 or 2 peices of gear with a speed substat and that's it.  defense ring, crit damage amulet, attack banner.  makes it super easy to build in my opinion since it's gear you'd never use on your other champs.

mine isn't perfect but he can 1 shot the first 2 waves and 2 shot the last wave making it 6-7 second runs in 12-3 brutal.  my masteries aren't maxed either, no gold scrolls, but have the rest. the QOL was worth it.

Thanks, this helped a lot. I'm down to 12 seconds (short some needed gear). I can 1 hit the first 2 rounds, the final round takes an extra hit.

6 star gear, crit dmg gloves, attack% chest, and attack % boots. Only need over 110 speed to be faster then the