The mixed voting system in Germany is definitely seen as a pure proportional system. A proportional system comes with problems. For example, if there is no quorum, no internal limit, there will certainly be a large number of parties. Quite often, you will end up with an elected parliament that is absolutely impossible to control. That is what allowed the rise of Hitler, by the way. It can go that far. But the Germans understood something at the time.
With a pure proportional system, there is a real danger that there will be confusion in the parliament. At times, there will have to be a “referee”, someone who really holds the power. So, at the time, the Germans decided to give the president of the republic the power to make decrees. It was as a result of that confused situation that Hitler began his rise. That is not a good way to go.
The other way is to cut from underneath. I think we can do better than that. There is no reason to cut off the Green Party. In the German system, the Green Party would have no seats, unless they got three members elected.