I mean, yeah they seem to be ass holes so far. Like, training sounds excruciating from MC's words, but wouldn't that kind of abuse be necessary to get strong enough to kill the demon king? I mean, their attitude obviously doesn't help but come on. If the goddess is right about how they were still sane people, I doubt they had any really malicious intentions from the way they treated/trained him. So think of it like this, MC got carried in a sense, to the point he got strong enough to back stab his teammates to take most of the glory. Does that really justify his side too? It's pretty clear it's a bit of both.