What is Vel'Koz's niche? Damage? Nice niche.
The reason Vel'Koz is fun to play AND balanced is because he is INCREDIBLY EASY TO BE BALANCED.
Look at his kit:
Passive: After dealing damage 3 times, the enemy takes more damage.
Q: Send out an orb, dealing damage and slowing.
W: Send out a fissure, dealing DAMAGE!
E: Break the ground at the target position, dealing DAMAGE and knocking enemies up.
R: Channel for a few seconds, shooting a huge laser that deals DAMAGE and slows enemies hit.
Wow, look at his abilities. We have passive for bonus damage, a splitting skill shot that does damage, an AoE skill shot does damage, a delayed area of effect that deals damage, and a channeled ultimate that deals DAMAGE. Wow, I can feel how unique Vel'Koz is!
Let's be honest here, if Vel'Koz was imbalanced right now, then Riot would have failed at the easiest champion to balance in the game. Tune the damage to be right and WOW, he's magically balanced.
But what am I even typing this for? Ignorance is bliss and those that love Vel'Koz love him. That's fair, it's fun to see those big damage numbers. But Vel'Koz isn't accomplishing anything Xerath, Veigar, Malzahar, Brand, Cass, Annie, Anivia, or Viktor aren't also doing with some other things. Vel'Koz is balanced and fun to play because it's almost impossible for him to be unbalanced and not fun to play since his balance is basically just a damage meter that you can pull up and down.