Luneth is one of the four Warriors of Light and is the first character you can play in the beginning of the game. He is the first to be chosen by the Wind Crystal. Because of that, it is entirely possible for Luneth to blaze ahead in the early-game as a more powerful character, but by the endgame this has pretty much become moot as everybody else in your party catches up.
Due to the fact that stats are more affected by the jobs you pick than the characters themselves, characters are as valuable as you make them out to be. Additionally there are only four playable characters and all four are out in combat all the time, meaning you will have no issues with keeping everybody leveled. However, Luneth is the most well-rounded out of the group, which makes sense given that he is the first character you can play. His stats are all solidly average which makes him readily adaptable to any job you put him in.
Luneth, as a result, will excel in any job given to him so long as he invests in the job. I recommend you start out with Red Mage and then progress from there to jobs like Dragoon or Black Mage. Due to the jobs affecting stat growths the most strongly, you should aim to focus entirely on either magic or melee.