Yes, I agree with you, more is going on than can be accounted for by a strong will. It would help clarify the situation if you could arrange for a broad evaluation by a developmental team: developmental pediatrician, developmental psychologist, child psychiatrist, speech/language clinician, occupational therapist. These various professionals can collaborate with the pediatric neurologist. The medication your son is taking to treat his seizure disorder could well have a stabilizing impact on his behavior, but it does not appear to be doing so. This in itself warrants additional evaluation.