Here are some that really bugged me.
Xander-"Let me blindly follow my evil and goopy dad!" I really hate how, even when his actions kill his little sister, who he supposedly cares about, he doesn't change.
Hans-A bandit who somehow managed to get himself promoted to a secondary villain. Lacks any charisma or intimidation factor to justify a role more than "show up in one level, get killed".
Iago-A poorly written antagonist who has no real reason to hate Corrin, but spends his entire life trying to kill them.
Soleil-Because sexual harassment is funny.
Sylvain-He has a tragic past, true, but that doesn't absolve him from being a jackass to the women he dates.
Leonie- "You really don't appreciate Jeralt enough. Now, let me tell you how much I want to bone your dad".
Cyril-He's bland. And his main character trait is wanting to bone Rhea. Would anyone really care if he was removed from the game?