To be fair, you drag Arden across an entire FE4 map and tell me you're still sane. Even then, it's more like 50% at most if you consider the number of characters that don't get a horse until after promotion, and then it's never really 70%.
And as for pointing out that the class structure is bland in general. Well yeah. But more than that, there are only 6 Pallies. Even if characterization is a bit low in FE9, you have about 35 other options that will all allow you to complete the title.
And as for being more useful than 80% of the characters, it depends mostly on how you play. Though I'm sure I could name 10 characters that are more useful.