Personaly I think Legate Lanius is over powered considering his sword out ranges all my melee weapons and he is faster then me (he is wearing a ton of armor how is this possiable) and I didn't train in melee weapons so I can't do alot of damage and my robot dosn't do any damage because shooting him dosn't hurt him (dosn't make scense) so if im the only one who is having troble on this then don't change him lol, but if someone who beat him or someone could help me kill him that would be nice. ( I have tryed to kill him now for 2 hours) Maybe im just dumb and there is a way to kill him that i'm not doing any help would be really nice thank you.
(P.S. the speach path where you can not have his gaurds fight you is amazing but sadly my speach maxs at 92

Have you tried armor piercing ammo on him?

No, thats a good idea I found out that a sniper works really well though and that you can shoot him it just can take awhile with out armor peirceing bullets, so he isn't over powered.

I used a .50 Anti-Materiel rifle, boosted with a few psycho's, a few jets and some steady. Walked to a place where I wasn't detected and VATS'ed him with a sneak attack critical. Took away 75% of his HP with the first shot, lady luck popped out and [censored] him up, and I finished him off with a second shot while he was on the ground.