this. loudness in restaurants/bars/etc is a feedback loop. It's loud so you talk louder. It gets louder so other people talk louder. repeat.

Being slightly deaf in one ear, I’ll tend to speak louder and louder to overcome the noise level in a restaurant to the point where I lose my voice.

That's my point - often just treating the reflections form the ceiling alone isn't enough, you need to stop the reflections from other surfaces as well.

Other reflections may be desirable as masking noise or to create a particular ambiance. Or not. That's part of the experiential difference between a lively bistro and a bordello style steak house.