Op. I’m not sure of your point on if the school told you he’d walked out of isolation you’d have dealt with it. He’d already done it the moment he walked out the door, there is no genie that can be put back in the bottle at that point, the crime had been committed,
he refuses to go to school, you’re his parent,he disobeys you and doesn’t go. He shouted and swore at a teacher, he refused to leave the classroom, disrupting the lesson for everyone else. Those children are entitled to a calm and safe undistrubed learning environment. He then walked out of isolation, his punishment for what he’d done, thus refusing the punishment.
what else were they supposed to do, talking wouldn’t make it better, or change it, it would have taught him nothing other than he can be aggressive, abusive and disobedient and mummy will sort it for him, and he then gets to tell his mates how he got away with it as mummy sorted it.
he needs to face consequences for his actions. It’s good he feels embarrassed, I’m sure it’s very cool to just refuse to go to school when he fancies it,spend the day round the house and just lose a few privileges like his phone or game. It’s very different to when the school say you’re not allowed in and he’s punished in front of his mates for his shit behaviour.
you should be pleased the school have acted, as your punishments and talking don’t work, he blatantly disobeys you,
so if he continues the next step will ultimately be expulsion and move to another school. Shit jobs earning no money as an adult. Poorly educated and unable to have any money to go out with his mates, go on holidays, get a car. I’d be making it clear what his actions are doing to his future.
so no, I’m sorry the school shouldn’t have went easier on him. They stepped in just as they should have.