So if he was as great as people say he was, then he would have intuited the fact that his son would eventually turn out to be a bad emperor, and would have murdered him? Hmmm...
I don't think most people would consider inability to predict events that will occur after your death, and the act of not committing filicide to be very serious character shortcomings.
Commodus renounced Stoicism after his fathers death, and didn't do any of the terrible things he was known for until after then either.
This argument is beyond weak in terms of criticising Stoicism or Marcus.