Exactly. That was the whole point to Unbreakable. Glass operated off the idea that if he's so brittle, then obviously there's someone out there who is nigh indestructible. It's what lead him to cause all those horrific accidents that ultimately lead him to Willis' character.
While Glass' condition is medically known, Willis' condition wasn't. Even Willis' character wasn't aware of the possibility, despite having a lifetime of experiences prior to meeting Glass (Including a major auto accident where he ripped off a car door). Same with The Horde (McAvoy's character - I wikied it). His multiple personalities are a known, medically accepted condition. The fact one of those personalities turns him into a super powered monster wasn't.
It's internally consistent logic for the setting, that yes make Glass a super individual for this setting. Glass has never shied away from the fact he's a Villain. Says so right in the trailer to the Beast "Sounds like the bad guys teaming up."
Samuel L. Jackson's Mr. Glass is one of the most compelling super villains that has never been put to comic format. So yeah, he belongs in that group - especially since it was Willis' interactions with him that pulled Willis into the "delusion".