Defiance Banner making my friend lag

This is a shot in the dark, but I'm playing a tactician banner only build with my best friend. I played acts 1-4 with a grenade build for a smoother leveling process, then in act 5 I converted to an all banner build and whenever I buff him with Defiance Banner, it lags his entire game to the point where he just teleports everywhere on his screen and it's borderline unplayable. All three banners make him lag, but Defiance Banner is by far the worst offender. I was wondering if anyone has a fix? Another thing to note is that he says it feels like ping lag and not fps. The banners are causing him to rubber band all over his screen.

Extra Info: My Defiance Banner is socketed with Refraction and Magnified Effect. Also, he's playing Smith of Kitava with Resonating Shield, Boneshatter, and Sunder as his main skills.