if the loads were equal, they would presumably both see about 200V between their Phase and 'neutral'.
Kind Regards, John
Equal loading being the critical point here, If there is a significant imbalance in the loads on the three phases as is often unavoidable, especially with portable/temporary installations, then the un-referenced "neutral" will float around in proportion to the loading. You effectively have a three legged potential divider with a floating centre point. In theatre lighting, where the load balance often changes significantly with every scene change, this can be particularly disastrous.
I've seen it happen a few times, one of which involved about £50k worth of intelligent lighting releasing it's magic smoke.