Sevarog's usually have ridiculous armor, so you need Buckshot. However, getting in close for a Buckshot leaves you open to a Subjucate or Phantom Rush followed up by a Siphon. Keep "Move Along" ready for this. Also try and put a Trap between Sevarog and you, so he has a harder time closing the gap. Never let him get close or he will ruin you.
Murdock is a crazy damage dealer who will give Sevarog a hard time if he is far. If you are Murdock use buckshot to lower defense and then use your normal attack or use move along to make him move away. Use a trap for the best use so that he doesn't get close.
Well with Murdock's abilities reworked I think it changes your tactics a little bit. As an experienced enemy Sevarog their build will likely compose of basic armour and/or ability armour. Murdock can quickly burst down targets and is a great way to bring down Sevarog, keep in mind I wouldn't recommend having a 1 v 1 with Sevarog. Have another tank be with you to avert the attention to your tanky team mate not to you. Keep being on the edge of fights and keep hitting him with your basic attacks, your buckshot knockback will keep him from getting close to you, hope this helps!