To be honest I don't care enough about, nor have enough time to continue, this seemingly pointless discussion. As someone on that forum alluded to, the specific categorisation of this line is not important enough to warrant fierce debate. While it is obviously a light rail line, as evidenced by its complete lack of level crossings and sharp turns, the small number of people who would benefit from the small extra convenience of seeing it labeled as such on OSM is not significant enough to warrant a war. To those who ignore evidence and preexisting examples of this exact type of system being labeled as light rail in OSM (in of Köln, Dortmund, Essen, Duisberg, Northeastern Paris, etc.), you win. Have a nice life and be content in the 'knowledge' that your favorite Poznań does not, in fact, have light rail.