Well if that's the claim, it's still wrong. There had already been four Superman movies, and the fourth Batman film had come out a year before Blade.
The Superman and Batman movies had become a joke in the early 80s and early 90s, respectively. The Superhero genre had failed to take off prior to Blade and X-Men. The fact of the matter is that those two movies paved the way to the modern Superhero genre. I'm fully aware that more successful ones came later, but that's not how I understand the claim made in this thread.
Both "X-Men" and "Blade" made LESS than "batman returns" and "batman forever." Far from "becoming a joke," "Batman Returns" and "Batman Forever" were successfull blockbusters. Only "Batman and Robin" was a bomb, and that was '97.
"Blade"--- $70 million 1998
"X-Men"--- $150 million 2000
"Batman Returns"--- $162 million 1992
"Batman Forever"---- $184 million 1995
I can maybe buy the argument that "X-Men" got the foot in the door, but I don't buy that it was "Blade." It wasn't a blockbuster, wasn't thought of as a superhero movie, and was R-rated.
I still go with "Spider-Man" starting the modern wave.