He could have treated Charles badly just as a result of his being such a dolt. Charles, that is. Hard to be a manly man and war veteran and raise such a turd, I would think.
Charles was - and this is fairly well-documented - a somewhat sensitive child - and Philip - who everyone agrees is not a sensitive man - forced him into his own beloved old school - the dour Gordonstoun. Charles hated it (I think he was bullied) but was not allowed to attend another school. Philip also berated and belittled him on a regular basis. His daughter Anne - a remarkable lookalike - was his darling. Prince Charles - as a very young man was not really a bad guy. He got truly bizarre and awful later on. He aged 30 years just being married to Diana, lol!