They mentioned he wasn't much of a scientist. Their goal is also to focus more time on lesser known characters in the history of science instead of being just another show talking about Galileo and Da Vinci.
Also Macfarlane essentially paid for it, and used his pull with Fox to get the show made, he wasn't writing for it. Brannon Braga from Star Trek is the director, Carl Sagan's Widow, a couple other former writers of the original Cosmos, and Neil deGrasse Tyson worked on it. It's also absolutely delightful.