Where I live, the classification of bikes in just 3 groups is not appropriate. We have road bikes with flat bars, that some people call a hybrid. But we also have bikes with front suspension that are not MTBs and are called hybrid by some. The flat-bar road bikes seem to be as fast and light as a road bike. The ones with the front suspension are heavier but also reasonably fast. The big difference comes when you start to get the wide chunky tires. This gives you not just increased weight but increased rolling weight and gyroscopic effect. So the bikes with heavy wheels can't accelerate or brake so easily. In addition the chunky tires flex considerably as they compress under the weight. This compress-decompress action takes a lot of energy. I frequently find myself coming up behind a dude on a commuter bike with heavy tires, and while he is constantly pedaling downhill a slight gradient, I can just coast past him.