In a 2017 interview about the making of Hollow Knight's map , designer William Pellen told me that Team Cherry "shied away completely" from describing the game as a metroidvania. Artist Ari Gibson added that they didn't want to "let a genre dictate" the decisions they made about Hollow Knight's design while they were making it.
And yet judging by its place on Steam, Hollow Knight is not just a metroidvania, a specific subgenre of adventure game defined by nonlinear exploration and gaining new abilities that gradually grant access to more and more of the game world. It is now the Metroidvania.
Sorting the user-applied Metroidvania tag by rating on SteamDB, Hollow Knight is on top at 96.08% positive, just a hair above Dead Cells. By followers it's also #1, with its upcoming sequel Silksong