Speaking of Johann, more and more I'm suspecting that he has a fundamental lack of flexibility in how he works. Not just with his magic, but with his approach to everything.
He struggles to learn magic outside a narrow remit. He struggles to learn languages (and one suspects learn in general, considering his comments on normal research) in formal environments. When he got stuck on the problem of the Ratling gun he got completely stonewalled without Mathilde's help, and his solutions to dealing with it on the battlefield were just applications of tools he already knew rather than anything innovative. His approach to combat is simple, basic, and straightforward to the extreme.
Now, this isn't strictly a criticism of Johann; he's very good at what he does, I'm glad to have him with us, and it's not like being relatively inflexible is a crippling issue. But it is something I've noticed and felt worth noting.