In order to avoid his snake stun, use your escape ability to the left or right. Don't draw back, since his snake travels much longer than his LMB attack.

don't try to repeatedly stun the enemy because the enemy can be stunned only every 3 second(unless you're using the wekono's wrath legendary) and that goes for every enemy. otherwise it's a good plan to use your stuns in 1v1

Your stun interrupts Ruckus' minigun fire, forcing him to spin it up again from the start

ruckus doesn't have a shield in front of him that protects from stuns, so use your reload to deal with him. just avoid his high burst damage before you stun him, after that he has to spin his weapon for a second to get it back again.