Amarant Coral is one of the main characters of Final Fantasy IX yet he barely adds anything to the story.
There are some Final Fantasy characters who aren't as important to the story as others. This could be due to the fact that they are optional (like Gogo in VI or Vincent in VII) or that they join at a late point in the game (like FuSoYa in IV.)
He was originally a bounty hunter who ends u
joining the party out of a desire to become stronger than Zidane.
Amarant is actually a useful character in terms of his abilities, but he has almost no impact on the story. There are several more interesting characters who could take his place (such as Sir Fratley or Beatrix) and who would have a better dynamic with the party than the person with no personality and who has no effect on the outcome of the story.