It always looked like ds1 was the instigator in any playground stuff - until we finally unravelled what had really been going on when he went into year 3. Turned out he was keeping a lid on things for ages, until he really couldn't anymore and then blowing. In his case it was always a big emotional outburst, lots of shouting etc, rather than physical and it always looked like it came out of nowhere, because it would happen when he really was at the end of his rope after endless teasing and subtle bullying. He wasn't able to explain to us what had been happening before then and the bullying behaviour was easy to misinterpret as part of play, unless you actually stood and specifically observed them over several playtimes.
We do get playground issues from lack of social understanding and misreading others' intentions as well, but his reaction doesn't tend to be as extreme.
Ds wouldn't go in a room on his own at 6.5 either, the compromise was for him to sit on the bottom step of the stairs for 5 minutes, but then he was compliant and wouldn't get off the step if that was the rule - I know that's not the case for lots of other children. It didn't work as a 'naughty' or 'thinking about it' step as is often used for nt children, but it interrupted the behaviour and by the time he came back in the room things had moved on so it worked to distract him and halt the incident and gave everyone else 5 minutes to recover.
I totally understand about the computer time, I feel exactly the same and have often chatted with other parents on here who struggle with exactly the same dilemma. As you said, it's often the only break the rest of the family gets, so ends up being as much a punishment for everyone else as it is for the child concerned, but I do think it's a necessary evil, iyswim. We have known increments of loss and ds is always warned that he will lose X minutes of computer time, so that he is aware of the consequence of continuing his behaviour.
To be honest, it only took a couple of losses for him to decide it's a good idea to reign it in when he's been warned. He is a lot better now and very rarely loses the whole of computer time - if he does, it's usually because he is generally in a state and not coping due to other things. (This morning would be a prime example and he's currently a whisker away from losing today's computer time, but he has a stinking cold and is struggling at school at the moment, as well as being stressed and anxious about secondary transfer this year.) Even though we know the reasons behind it, we are consistent with the rules and consequences, because he needs the consistency and the shock of losing computer time is often what he needs to bring him back down again. Not to mention, we have a duty to take care of his siblings emotional needs as well as his and we can't support him and their expense, they need to know they can trust us to handle the situation and protect them.
I've probably worded that really badly, as I also have the same stinking cold and am really woolly headed this morning.