Human brain is way bigger relatively.

they're not

Dolphin brains are four to five times larger than would be expected for their body size when compared to another animal of similar size. In humans, the measure is seven times larger. "Essentially, the brains of primates and cetaceans arrived at the same cognitive space while evolving along different paths," Marino says. "What the data say to me is that we, as humans, are not that special. Although we are highly encephalized [have large brains], it's not by much compared with cetaceans."

https://www.nsf.gov/news/news_summ.jsp?cntn_id=100463

It's not the size that counts, but the plasticity.