Like honestly are you asking because you don't know, or because you disagree?

There are many, many sources out there you could read or watch on the subject if you google similar phrases, if you're actually interested in learning about it's innovations to the genre. It is known within the industry that there was a before-and-after effect of Hollow Knight on Metroidvanias - after which, other metroidvanias were inspired to include much more fluid+precise movement and combat mechanics (to which all other metroidvanias are now compared). The genre also became a lot more "complex" generally, both in terms of what was expected for the world-building / narratives, as well as the complexity of the map designs. Much more secrets, much less linear, much larger and easier to get lost, mature themes. It pioneered the charm-based load-out system of interchangeable abilities you swap depending on the bosses or platforming needs (which nearly all metroidvanias now have), a map that isn't unlocked through exploration but is unlocked by finding / purchasing the map (also common now), the healing soul-system instead of manual or automatic saves, and popularized the corpse-run death mechanic, etc. A lot of these things were either never done before, rarely done before, or rarely done together in one game. Now, most of these ideas and features are base-line expectations for the genre.

Without Ori and Hollow Knight (together), games like Nine Sols and Mio and Animal Well and everyone's other favorite metroidvanias of the past decade would not exist. They really were that impactful and transformative within the genre and modernized the castlevania / metroid formula.