Are you talking about standard attack or mystery? What lineup did your opponent had? We can't really know the reason why he hits that hard if you don't tell us the lineup.

Kazekage Gara is the most strong Kage when is about mystery , all people understimate him , people do not often use him because his mystery is 80 chakra and he shield ur team only if he has the barier , even without barier he is the strongest damage dealer, Even more than mei terumi , but she has more utility than him with ignite and poison .

Gaara shippuuden mystery is even stronger ;-P. That said, is not true at all that his damage is so op. You get a 5k on a crit if you have boosted him with bee, wind enhancement and the barrier is up and still, for example, in the same team sage naruto mystery do about 20% more damage. Tenten gnw with only the barrier of mei and water enhancement do the same 5k in round1 if doesn't crit. The same does a tendo boosted in an mb team with wb asuma and a 2nd booster.