You are correct about this:
"As to the need for dark matter, I thought there has been some astronomical
evidence for dark matter's existence. Wasn't there a case of two galaxies
colli
ding and the dark matter partially detached? Essentially there was
evidence for a large gravitational field not associated with normal matter."
Comment: Before a physicist whose experience is mainly limited to universities pontificates about the universe, the physicist should first consult an astronomer.
Comment: Not everything is relative. Galileo showed that if everything in the solar system went around the earth the phases of Venus would not be what he observed.