While the announcers are hired by the teams, they do vary in how biased they are.
Vin Scully always does a great job of calling the game no matter how the Dodgers are doing. Most are homers to some degree, but are honest about the other team.
Personally, I only like watching Harrelson and Stone when the Sox are losing. The Schadenfreude of listening to a sullen Harrelson is worth the price of admission.
Take the Indians this year, PLEASE! They went from first to worst in a matter of weeks. Now they where not that good of a team to begin with, but I would expect the local broadcast to portray the slide in realistic terms and to have empathy with their fellow fans. After all, they are going through it right along with the fans.
Harry Carey was a great announcer for the Cubs, even when he was hammered up in the booth. Years ago my younger brother was an Andy Frain at Wrigley and his most important job before all home ball games was to make sure Harry’s fridge was stocked with Bud.
I remember watching a Cubs game years ago when Harry was more popular than “Da Mayor.” with Harry and Steve Stone....Cubs are at home, it was the top first, the Cubs pitcher has bases loaded, nobody out and walks the next batter. Stone says, “Well Harry, it’s one to nothing.” And Harry says, “Get the bum outta there, he’s stinking up the joint.” Harry called it like it was didn’t care who he offended. That’s also the reason the White Sox fired him. He was brutal on the White Sox the year they fired him and Jimmy Piersal.