They actually have a decent case here.
They've been a band with a trademarked name for 25 years. Netflix used that same name as part if the movie title. The band can show measurable harm to their trademarked brand, by citing Google search results for Demon Hunter.
I can't imagine Netflix would change the name of the movie, but paying the band for the damage to their trademark, and compensation for having to rebrand and trademark a new band name is a reasonable cost of success for Netflix.
In short, it isn't very Oniony