Dealing with thought only in abstract often ignores real world consequences of that thought system. It makes sense to ask what part of that thought lead to different behavior in real world.
It's not enough to dismiss the philosophy, but parent comment is absolutely correct that you should keep it in mind as historical context.
Of course, to not hand power to Commodus would have meant his death. I'm not judging him for his decision, but given his absolute power and obvious clarity of thought, it was a conscious decision to choose his son's life over the good of the empire.
The generally contrived nature of this argument aside, this is really just revisionism. Commodus was 18 when Aurelius died, and he didn't become a lunatic until a fair bit after his fathers death. If you're looking for flaws in Marcus Aurelius (there's plenty), this isn't one of them.
It's easy to get swept up in Meditations, viewing Marcus as the stoic Philosopher King that has profound lessons for us even today.
Parent tried to remind everyone about Commodus, and in my opinion correctly so; if Marcus lived up to the myth surrounding him, he'd have intuited the situation and dealt with it.
But he either didn't see what was coming, or decided to do nothing. Because for all the hype, he was just a man. Keeping this in mind is an antidote to getting carried away by what is a genuinely compelling piece of writing.
I wouldn't make this argument in a vacuum, but I saw OP get downvoted and wanted to jump in because I thought it was a fair enough point.
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.
If the argument were that weak, you wouldn't bother with the strawman to counter it.
He raised Commodus, and co-ruled with him for a time. - He was was either unaware of his son's (lack) of fitness or - He was aware but unwilling to take corrective action or - He was aware but unable to take corrective action
Probably that's still kinda true for most people who have kids but are famous for accomplishing just about anything. And anyway even poors pay for childcare now, what with two-income households, and between that and school end up spending maybe 1/4 of their kids' waking hours even kinda near them, at best, and much of that occupied with meals and morning/night routines (so, a good bit of it the stuff people who can afford it tend to outsource, though also they usually outsource a good deal of cleaning so the time-spent-together may be a wash), so maybe a little instruction by example but little time for anything like serious coursework or major instruction from parents.
It's useful to keep this in mind when reading his meditations. Yes, the message can be nice and joyful to read. Yet the man who wrote them created a tyrant and contributed to untold suffering.