Our ruler would be Jim Morrison.
(I googled but couldn’t find a suitable audio clip)
Bird brains are organized very differently than mammal brains. There is some evidence that they do more with less.
Caledonian crows have much smaller brains than chimpanzees but show comparable levels of tool use, including modifying items to make tools, and problem solving as just one example. That’s partly due to having a small body mass, but not entirely. Just because our brains work well enough to enable civilization doesn’t mean they have the most efficient design. Again, evolution doesn’t give you the optimum solution, as long as it gets the job done a jury-rigged mess will endure.
Flightless birds can be quite large, especially before humans arrived on the scene. Like the terror birds. Or ratites.
Granted. However, it would take a relatively longer time to “turn the ship around” and head the opposite direction and evolve bigger brains. Primates already started out with bigger brains.
Oh, definitely. However, having that small brain still makes it less likely that you’ll evolve sentience within a specified time frame. Primates never had that hurdle, which is a big reason why we got there first.