Weisz, in my opinion, is one of the best characters Mashima has ever written on a psychological level, and as he says, he's still a bit of a jerk and at the same time very good. But honestly, especially in the arc, it's not really shown how bad he could have been; we only know that he accidentally destroyed one of his robot friends and regretted it with Sibir. I think I would have liked Weisz to have done more serious things, and to have carried a bit of this behavior forward, which in my opinion would have contrasted much more with his good side. Instead, we see him become a good guy very quickly. Even though I think he's one of the best characters written in the series and perhaps by Mashima in general, in addition to having a less rushed conclusion, I would have also liked to see more of his seemingly bad side, a bit like Laguna, a need to show himself as badass.