Yeah, I don't see this hate either. Sounds like hyperbole to me. Erdrick at best will get a "who?" reaction from a bunch of people.
The hate was against FE, not sword users in general. There's a severe minority that doesn't like "anime sword users", yes. The minority that dislikes the high amount of FE is actually bigger than that. The issue doesn't honestly exist. Plus, anyone causing that much trouble is the problem, not the character. Mind you, I don't believe Erdrick is a guarantee, but I don't think he'd sell badly either. I can understand if they used a more worldwide option, as they haven't shown anything to imply they're grabbing a single character for advertising(Corrin was partially about this), meaning there's a lot of potential choices. Ones like Slime or Sora, or even Sephiroth, are very well known worldwide and could easily fit that factor and be the specific character. Though Brave, if it's meant to be them, doesn't tie well to Sephiroth. The rest well enough(if Jack is meant to tie to Joker, as there's more than one way it can reference the character. That means that Brave can be used multiple ways too).