User blog comment:B214/Question and Answers 6/@comment-190.164.227.239-20161201033222/@comment-1359322-20161205095743

Another interpretation we can take is from what Ddraig said early in the story, most of the past possessors view him as a tool. In that sense, Ise may be called the weakest not because he's weak but instead of fighting using the BG, Ise fights alongside the BG. Like maybe most possessors can fly without Ddraig's help but Ise needs his help etc. In short, Ise's usage of the BG is dependent on Ddraig's assistance something past possessors didn't need to do.

Then again we don't know how strong Belzard actually is, well if we take Vasco serve as a standard bearer, Belzard might be someone capable of taking on a God or two but he opted not to. There's no rule that says Longinus users must fight Gods after all.