MZ's have to be the only manufacturer of the period to recommend such a lean mix of oil. I'm not saying it's wrong either way. A lot of people love their 50:1's. Different bush vs bearing types are one of the reasons for the leaning out. Not to do with combustion. But, speculation at the time also says that being that Eastern Germany was predominantly 2t vehicles (and especially in the cities that can be congested), lowering the consumption of oil was better for the health of people in the cities. That could be a big reason. Not sure. I don't care. Some people measure out their oil to the exact Millimeter spending half an hour at the petrol tap.
MZ aren't as infallable as a lot on the German forum make them out to be. Their manuals are full of mistakes (for example seeing as you mention it, they can't make up their mind whether the gearboxes for ETZ250/251 hold 900ml or 1,000ml), and like any company sometimes they make decisions, or get told to make recommendations they might otherwise think is actually not good practice, esspecially in the long run - otherwise they're fined, or such like. Car manufacturers now 'recommend' that their gearbox oil NEVER needs replacement, and also the engine oil interval is 20,000 miles! Would you follow that?
People think way too much into this sort of stuff and there are countless arguments for and against lower or higher oil consumption since the combustion engine was invented. I say just research as you please and try and get the best opinion you can from your own perceptions so long as they're not wild. A lot of MZ riders these days tend to meddle with their bikes and shoot hot air, speculation and theory and semantics more than actually ride them- so they'll never see the effects either way of using 50:1 for that 1,000 miles over the 10 year period they had and used the bike for...