This troop seems quite weak. You tried to compensate it's low damage per second with really high range and the ability to jump over walls, both of which are great although there mightn't be a need to jump over walls if you have massive range and are following tanky troops who will destroy walls for you.
However, it has a really large housing space for the amount of DPS that it brings (2 damage per housing space at max level). This is comparable to a golem (1.8 damage per housing space at max level) which is a troop designed to be tanky.
Another issue with your idea of the Centaur is that it has plenty of defensive weaknesses, but most notably its weakness against the mortar - it can be one-hit-KO'd by a level 7 mortar at max level. I don't think these weaknesses are necessary given its relatively poor offensive state.
Finally, its poor aim makes the troop unreliable. It would make using this troop more about luck rather than skill: even if you deploy it well, it might still decide to do its own thing (much like how the AQ has a tendency to target walls... :P).
With all this in mind, I would:
a) Increase its DPS significantly (I would make it something like 144 damage per second, 72 damage per shot at max level)
b) Lighten the weakness against the mortar (2x damage maybe)
c) Make it more accurate.
Hope this was helpful advice, feel free to object to anything I've said if you disagree
Just to clarify, new troops are definitely not ruled out, what you are looking at is the list of ideas that have already been suggested (the top half or so).