Sydney's shots are impossible to dodge if the other player know's what he's doing. Try using it like the BFG or Rocket launcher in Q3 and you'll know what I mean.Patch's shots aren't hitscan, unlike the chaingun officer's. Therefore he's not really useful unless you're up at close range.
Patch and C.Blackhand's clip sizes are puny for the rate they fire at, while the damage per shot is relatively weak against vehicles. A rocket soldier will do more damage to vehicles at a cheaper price.
Patch/C.Blackhand really don't have anything special going for them to justify the $450 cost.