Before humans evolved, dolphins were the smartest species on earth, smarter than great apes, parrots, crows, ravens, monkeys, and elephants. There is nothing wrong not being the absolute best in the living world, because only one species can be the best in anything, but there are millions of species alive. The only thing a species has to do is to be good enough to survive.
Scientists do not measure the number of neurons to determine intelligence, because the larger an animal, the bigger its brain tends to be. Of course that does not mean that dinosaurs had larger brains than we do. They don't. Dinossaurs are pea brains, but if you compare a small dinosaur with a large one, the larger one is likely to have a larger brain, because larger animals need more brain cells to control their larger body. However the brain also increases in size more slowly than the body, so if we go by pure brain weight to body weight ratio, then it won't work either. That is why scientists come up with a new measuring method, known as EQ, or Encephalization Quotient. It is not pefect, and the largest animals still show a relativley low EQ even though they are more intelligent than their EQ suggests. Using EQ, humans have a higher EQ than dolphins. Since most dolphins are in fact larger than humans, they tend to have a larger brain, but when we factor in the fact that larger animals have larger brains, dolphins actually have a smaller brain compare to humans if they are both the same size.
Even though we have the most intelligence of any species on earth, we did not accomplish much as a species until after the end of the last ice age 13,000 years ago. Before that, we had nothing except some cave paintings and some artifacts like a flute made of bone and some stone tools to show our intelligence. That is because we mostly used our intelligence to find food, just as dolphins do. Only after we invented agriculture and were able to devote more time inventing new things did we advance as a species technologically beyond the stone age. We also have another advantage over dolphins, our hands. Dolphins have flippers and they simply don't have the ability to build tools the way we can with our hands. The most the dolphins can do to show their intelligence is to blow and play with bubbles in captivity.