To its detriment, I would say, the power scaling is almost non-existent in Boku no Hero. Bounties, chakras, Nen or what have you exist (or rather persist) for a reason in shounen series. Without some baseline 'power' or 'strength' measurement, the fights are relegated to pure ability dynamics that can be hard to follow, and have also led to quite a bit of discussion and criticism in this very thread (like why going through concrete doesn't kill a person automatically when their quirk has nothing to do with body strengthening- because a baseline of quasi superhuman bodily 'strength' has to be assumed since the story does not provide one).

I don't know if the author sidestepped that shounen staple on purpose or what, but the result has certainly changed the... texture of how conflict battle can be resolved in HeroAca. On the one hand, clever power usage means you can pull underdog victories out of tactics and environment alone; Hunter x Hunter exceled at this. The downside to this approach is that you, as the writer, have to be at least slightly more clever than whatever your audience comes up with for power application or they will begin to second guess you and the characters(also can be seen in this very thread). Anchored power values streamline this process and bake in some wiggle room for matchups.

I mention this (which is news no nobody here) to juxtapose that the villains we have been exposed to in MhA aren't necessarily the de facto most dangerous ones, as that is purely decided by the usage of ability. I would personally be the most afraid of the mind control kid from season 2- he is basically Kira if he wants to be, or Mirio when he could permeate. Horikoshi, the author, no doubt takes some inspiration from western comics in crafting his superhero tale, but that format of storytelling is very much not traditional shounen in structure, so compromises were clearly made. Weekly Shounen Jump isn't interested in Peter Parker being Spider Man; it's interested in his training arc with Uncle Ben before he gets killed off in the 'late for dinner' arc...

We simply are expected to take at face value who is the most dangerous villain according to the story, but we aren't given self evident reasons to believe it.