A similar discussion is going on Twitter right now, and amazingly since 2006 nobody's mentioned the word Frischkäsezubereitung. That's what the Philadelphia brand sells here in Germany, but you have to look at the ingredients list itself to see it. I'm convinced that's the issue and not the Doppelrahmstufe. In fact, the Philadelphia brick in the US has 35 grams of fat per 100g, while German Frischkäse tops out at 27g fat in the brands I looked at in this spreadsheet - and the Philadelphia Frischkäsezubereitung only has 21g.
Thanks to @ellbie for confirming that draining water from Frischkäse and maybe even Frischkäsezubereitung worked well for cream cheese frosting, too. That Milbona brand has the highest fat content I've seen in Germany... 28.7g!
https://www.cynthiabarcomi.com/buecher might be useful too. The American mentioned above who has a whole book dedicated to baking cheesecakes in Germany.
And there's a whole thread about baking cheesecakes in Germany with notable successes: https://www.toytowngermany.com/forum/topic/18089-baked-cheesecakes/?page=3#comment-1547868