Galileo addressing Orazio Grassi ("Sarsi"):
> You cannot help it, Signor Sarsi, that it was granted to me alone to discover all the new phenomena in the sky and nothing to anybody else! This is the truth which neither malice nor envy can suppress!
There were plenty of people working in the field (most well-known Harriot, Marius, Fabricius, Scheiner), but Galileo does not seem to have thought much of them.
Grassi published a work on comets in 1618, and Galileo read it. We still have Galileo's copy, which in the margins has the following notes: “piece of asininity”, “elephantine”, “buffoon”, “evil poltroon”, “ungrateful villain”. He was not a fan. (Grassi was more correct on this topic.)
For all of Galileo's intelligence, he was a somewhat of an ass, and alienated a lot of people. His Il Saggiatore (The Assayer) was an attack of Grassi's view; Grassi responded with Assagiatore (Winetaster—insinuating that Galileo was drunk when you wrote his book).
Academics (and politics) was a blood sport back then.
Galileo did a lot of good work, but at the end of the day, I'm not sure we needed him for progress to have been made. The word "revolutionary" being used towards Copernicus' heliocentrism is probably warranted. Tycho Brahe's hard work in making observations were key in the effort, and it was Johannes Kepler's idea of breaking free of circular orbits (that everyone else was using) over to elliptical ones that was a real innovation in modelling.
(Galileo preferred the Copernican system, while Grassi preferred Tychonic. Kepler, with elliptical orbits, ended up being correct.)