The only legitimate reason to rank Waldner above Wang LQ or Wang Hao is a question of who he had to beat to win his championships. In his day, he had to beat the usual number of amazing Chinese players (which started with Jiang Jialiang and included Kong, Wang Tao, Liu Guoliang, and even Ma Lin). But in addition, he had to contend with a much tougher generation of European players than there is now. Think about who the European players were that are about the same age he is; Persson, Gatien, Saive, Korbel, Primoracs, Kalinic, Grubba, young Samsonov, young Schlager, a somewhat older Appelgren, and many others, much tougher comparably than the European players of today. On the other hand, he never dominated the sport as completely as Wang Liqin and, Wang Hao have for stretches of years. Waldner did not always play that well in ordinary ITTF events and he was capable of losing to lower ranked people in a way that never happened with Wang Liqin or Wang Hao when they were having their runs. You could also talk about Waldner's innovations in the game, especially serving, returning serve, tactics, etc. But who before Wang Liqin ever played with that much power from both sides, and what penholder before or since has had a backhand and a return of serve like Wang Hao?
It has to come down to those three, but like I said, there is no one obviously correct answer.