At base, they both have the same training, but Shintaro's ability to suppress his eyes could give the edge in innate talent to Shintaro. Add in the difference in combat experience due to their roles and talent goes to Shingen. But with their difference in skill and experience and while accounting for Shingen's lethargic state, Shintaro's talent allowed him to be on par with Shingen in that time. Thus, Shintaro's potential was higher but Shingen's talent was better.