It depends on what CBD apartment you buy. Buying your typical, run-of-the-mill apartment with no views and in a random part of the CBD will never go up as much as a well located, good quality/size apartment. It's just simple common sense!
People here are wary of OTP apartments for good reason. But I wouldn't be so quick to dismiss it - depends on what you want to do with it. If you get a decent place with nice views and can get a good yield, why not?