The grounded-ness matters too because it was, in comics and in earlier superhero stuff, the major distinguishing factor between DC and Marvel. DC had these epic, godlike, iconic characters, sure, but they often felt slightly mythic rather than relatable, despite some strong attempts. Whereas Marvel didn't have quite as iconic characters (barring Spider-Man, the X-Men, and arguably the Hulk), but it did have a universe that seemed more like our own, more relevant. They've lost that, and much as people might like, in the short term, movies full of whimsy and weirdness, and indeed, considered on their own, such movies may be strong, it detracts from one of the major selling-points. I don't think Feige and Disney/Marvel management really "got" this until recently.