D&D is indeed about roleplaying one's own created character.
Yeah, this just isn't true. At best, it's someone's personal sense of what DnD means to them.
In reality, there have always been pre-generated characters in DnD modules available for player use.
And yes, those pre-generated characters have often come with background and personalities.
It's just a fact, not even worth debating.
If someone doesn't like playing a pre-generated character, fine, whatever, to each their own. There's nothing wrong with that. But that personal opinion has zero to do with what DnD has--indeed--always been about.