Mom is shitty, too, yes, but dad is especially so. As I said in the previous chapter, he essentially alluded to the twins being a burden the MC when he loves and cares about them more than anything or anyone. Absenteeism is one thing, but to make such a gross assumption about his family when he's never around to know anything about them? He's a shitty dad.
Mediocre I agree, Shitty not so much. Maybe 4.5/10?
Reality is, Just because MC loves and cares about his siblings does not mean they're not impacting other aspects of his life and the previous chapters we see that his grades drop and before that he actively reject social invitations. If he just doesn't care about the social interactions that's fair, but if his grades are dropping because he was way too occupied with the twins, MC needs to show he can handle both responsibilities.
Hypocrisy much coming from him? Yes. Does MC still need to prove it? Also Yes.
The biggest problem with the father as a parent, is the fact that he was way too quick on giving him an Ultimatum and not trying to understand the situation or reviewing other options first. His grades dropping might just be a byproduct of the High-school environment, or something else unrelated to the twins but to be fair, it's a reasonable assumption.
That doesn't make him too bad though. The story frames it as the Step-dad felt guilt for suddenly popping up and making MC take care of his children. He's wrong but it came from a place of genuine worry;
the problem are the methods. What he needs to do is:
a) Make raport with his new Step-son and actually understand him
b) Just be around the house and understand the dynamic of the household
c) Find other options to help the kids out and communicate that to the kids before making any decisions.
He seems like the type in real life where I can talk to him, question his methods, and reasonably convince him that other options exist and he needs to to take a lot more steps before coming to a decision.
So all in all,
Mediocre but not as bad as some other people say.