@n0mesorah that is a valid point that he was no longer living when the school opened. But It doesn’t change the fact that he is believed to be behind the opening by his close student.
I think most readers of YWN are not interested in learning Mendelssohn’s teachings. So you probably should not bring up more questions about his teachings. At least definitely not in this conversation which has gotten very off topic.
I think he denied hashkafah that doesn’t make sense. But not halachah.