With the reveal of his (young) original in Union Cross, it's rather hilarious to imagine the grizzled and gruff voice of Shuichi Ikeda coming from the mouth of a teenage boy. Probably already weird for some that it comes out of a very pretty man like Marluxia, but somehow, I find that it works perfectly
It actually sounds to me like Keith Ferguson had a bit of a struggle to keep his voice that deep. It's definitely not what he's used to doing in roles, and Keith himself has a fairly high voice. So I can understand if he slowly moved up into a register he was more comfortable with. When Marluxia raises his voice, like near the end, it becomes a much more full tone. I think the only reason it's mediocre is because it's not what Keith was used to doing.