The downside of convolutional reverb is the lack of parameterization. You're kind of stuck with one fixed geometry of source, receiver and surfaces. It can also be expensive to apply in real-time processing.
A lot can be done post-processing the impulse response (volume envelopes, timestretching, combining with other parts, etc)
As for the efficiency: a modern laptop can easily run ~100 channels of multi-second convolution reverb in realtime on 44.1/48kHz sample rate and <10ms latency in real-time on 1 core.
Yeah, but if you post-process the impulse response, it's difficult to end up with something else that "looks" as much like a real impulse response. If that's important to you.
Don't get me wrong, I'm not trying to argue against using convolutional reverb. I was just throwing out a couple reasons why people still use other approaches.
As for the efficiency: a modern laptop can easily run ~100 channels of multi-second convolution reverb in realtime on 44.1/48kHz sample rate and <10ms latency in real-time on 1 core.