re: If we just lose Anderson and Gordon, what cap space would we have?

That's a pretty superficial comparison.

Posey was nearing the end of his career, he was 31, was strictly a "glue guy" type player, wasn't particularly athletic at that point, and was getting the MLE.

Barnes is 23 years old, was a high draft pick, is significantly more athletic than Posey ever was, and is looking at a huge contract. Barnes has had a higher 3pt% in his first 4 years then every single one of Posey's years in the league.

They really aren't the same player at all. Barnes is a major risk but his ceiling is WAY higher then Posey's could ever dream of, let alone at that point.