I agree with this. Given the circumstances, it would seem that dolphins are at a disadvantage to developing any type of society greater than the small pod communities they have now. Early humans were able to develop civilization, but first they found caves, they discovered wood, branches, etc, could build homes. Dolphins will never be able to develop shelter, communities, anything. Even if they were to try to live in underwater caves, they would still have to constantly rise to the surface to breathe. Humans never have to leave their homes.
Again, dolphins can't cultivate, they cant grow food, or raise cattle, they live in a 360 degree environment, how would they ever develop a large food supply for a massive community? It seems to me that it's pretty obvious that we were only so fortunate to have just the right things to allow our culture to evolve to where it is today. If the planet were all desert with nothing that enabled us to manipulate our surroundings, we would be just as nomadic as they, wild animals with an ability to understand local community and self. Oh you could teach us tricks too.