We clever primates rose to dominance out of the ashes of 75% of the species on the planet. It seems entirely possible that we never would have achieved this sort of reach if not for the K/T event.
65 million years is a long time even on evolutionary terms. Without K/T you would still have the dinosaur to bird transision because it's an useful nich to be able to fly. mammals evolved with dinosaurs and things may have followed a similar path even without K/T. However, Dinosaurs could have easily followed the same path as humans by filling the same ecological notch of squirls, then spider monkeys thus gaining thumbs to efficently climb with increased body weight. After that increased body weight and brain capacity are useful and suddenly your using tools.
PS: Birds have limited brains because of weight issues but their neurons are just as evolved and capable as primate neurons.
