But it doesn't send any message except to him and his friend. And even then, that message is "don't flame Valve employees because the ban will be much harsher than if you insulted a random person". If the OP hadn't took the effort to whine about being banned (in completely the wrong place and in the wrong way), nobody would know.
Yes, the guy who got banned deserved to be silenced, but not for 2 months unless he had already been silenced for 1 day, 2 days, 1 week, 2 weeks, 1 month, whatever. It can't just be arbitrarily handed out. Not to mention, I've seen things incredibly worse than what the OP said. If Valve feels their staff should be treated with respect, they should be identifiable.
The punishment for assaulting a police officer is much higher than a normal person, but that is only in the capacity they identify themselves (includes them wearing the uniform / badge). If they are in civilian clothes, they are just a regular person.
The Valve employee should have used the report system like everyone else. Either give them special colored names or a [Valve] tag or stop pretending they should be some kind of sleeper agents that can mute you for 2 months.