TripAdvisor has no credibility, THAT'S the point. Grand Hyatts or Marriotts are not luxury properties.
So, I'll pass on Grand Hyatts and/or Marriotts. However, we did enjoy our NYE stay at Park Vendome this Dec/Jan, but only because Meurice was sold out.
Do you consider the Vendome a 5-star property?
To each his own on Trip Advisor. It has helped me in the past, regarding that thread, I agree, it's well off the mark regarding luxury hotels in the US.
Which is why I included the Conde Nast reference. I think comparing hotel prices in Paris and Berlin is a mistake - Berlin is known to have some of the lowest hotel rates in Europe, especially for a capital city. Add the fact that you can get an off-season, govt, or book in advance rate at the Grand Hyatt for less than 200 Euro. It is a bonafide 5-star property, five stars staring at you when you walk in the front door.
Unless you're going by a master 5-star website I don't know about, I'd say you're basing your conclusions on personal opinion.