There is a flaw in your reasoning, which I explain below:
We do not need “only” 3 million years to reach our current level of intelligence, in fact 3 million years ago our ancestors or their close relatives were already building stone tools, that is, they already had a high degree of comparable intelligence.
At that time, the most intelligent species in our lineage were already on the transitional frontier between australopithecines and our own genus Homo, with larger brains than today’s chimpanzees and orangutans. They did not represent the beginning of our evolutionary lineage, as was the case with the first dinosaurs, but almost its end (taking our species as “final”, which is not exactly correct).
The lineage of dinosaurs, with its distinctive characteristics (two post-orbital cranial openings, shape of the articulation of the bones of the hind legs with those of the pelvis, hollow bones, undifferentiated teeth, etc.) 230 or 240 million years ago, from a lineage of more primitive animals that resembled today’s lizards (although not exactly lizards, as these belong to a different group):
These first dinosaurs were relatively primitive but evolved over the next 170 million years in a variety of forms, many of them already quite advanced, with almost all lineages (except birds) becoming extinct 65 million years ago after the fall of a huge meteor.
However, if we consider the animals of our own lineage that had the same level of evolutionary development as the first dinosaurs, we have to go back even further in the past, to about 265 million years ago in the middle of the Permian period, where the Therapsids appeared, creatures that they had only one post-ocular cranial opening but already had differentiated teeth as well as evidence of fur and warm blood (or at least “warm”, always somewhat above ambient temperature on the coldest days). They were creatures like the one shown below:
These beings evolved to become the dominant group of terrestrial creatures throughout the remainder of the Permian period, with a huge variety of species that already looked a lot like some mammals today, although they did not have all of their characteristics:
They only lost their prominent position in the ecosystem in the “Great Die”, the biggest extinction event in the history of multicellular life on our planet, caused by gigantic volcanic eruptions that ended the Permian period wiping out 90% of marine species and 75% of terrestrial species. Then, after a few million years of recovery at the beginning of the Triassic period, the groups of animals that survived this great extinction began to compete with each other, with dinosaurs finally gaining prominence only at the end of the period while the descendants of the therapsids were reduced in number. size and gave rise to the first species of mammals in the following period, the Jurassic.
Thus, if we count from the animals of our lineage that had characteristics similar to the first dinosaurs, we have actually been evolving for more than 260 million years, much longer than the dinosaurs had to evolve before disappearing almost completely and being once again supplanted by the descendants of therapsids, the mammals (which are to therapsids what birds are to dinosaurs).