Do you think we're just lying to you? Gilbert is a prime player in the Advance version. I won't disagree that he's absolutely abysmal in the original, but in the GBA version, he is a very useful character to have. His attacks cause great damage, and are great even in the back row. He can also massacre undead enemies. His Chant acts as a Mighty Guard-like skill, which is useful for boss fights, which was mentioned before.

And he has a pretty theme.

So, yes, he's a very great character.