Nobody can predict what will happen in the future - especially in this volatile industry. To make this type of decision, one needs to understand and then prioritize/rank the decision criteria...
Location seems to be one of the top criteria. With EW, he has a decent chance of ultimately returning to Germany which evidently is very important to him. With OS, there is a possibility he may not get the chance to return and live in the Hamburg area if he does not get the call from LH in a few years to transfer over (uncertain timeframe). In that case, EW makes more sense if he has more of a likelihood of returning to Germany. Plus he gets a more marketable type rating with the Airbus.
That is how I would evaluate the decision - to each his/her own...