Zaslav said this during his presentation at Cinemacon, "“It’s the best superhero movie I’ve ever seen. I have it seen it three times."
Gunn said this to the reporters while unveiling his DC plan, "“Can I say one more thing? The Flash is f**king amazing. “Like it’s one of the best superhero movies I’ve ever seen. [Director] Andy Muschietti did an amazing job.” He then tweeted the same thing recently too.
Then THR published that Tom Cruise article (presumably as promotion from WB) which said, "Cruise was so taken by what he saw that soon after, he reached out to Muschietti. It was a call out of the blue for the director. Cruise is said to have raved about the movie, saying something to the effect that Flash is “everything you want in a movie” and “this is the kind of movie we need now,” according to insiders.
Just today, THR published at report about how few WB execs are surprised by this promotion strategy saying "This has sparked bemused head-shaking from some at Warners who question the wisdom of setting such high expectations. “It can’t be the studio telling you it’s good; your friends have to tell you it’s good,” says one insider.
https://www.hollywoodreporter.com/movies/movie-news/the-flash-warner-bros-ezra-miller-1235509432/