There are numerous examples where Kennan's theory of containment was proven right, long before Mikhail Gorbachev came to power. While containment wasn't the only reason the Soviet Empire fell, it was certainly one of them, and was certainly a successful policy overall.
Consider the success of containment during the Berlin Airlift - where West Berlin was protected without ever going to war. The protection of NATO based on containment policy that maintained a communist free Europe for almost 50 years. The suppression of the Greek and Turkish rebellions, the Korean War, Quemoy and Matsu, etc. etc. At that time, in those places, the only thing the Soviets or their allies understood was force to defend non-communist territory, at the same time as not directly threatening communism where it existed.