Brown had a regression last season. His production was a result of him being forced balls by Big Ben to keep him satisfied. Throwing to Brown, Ben had a 61% completion rate and threw 10 INTs. Everyone else? 70% and 6 INTs. In a year, Amari Cooper has a very good chance to be a better WR than Antonio Brown, who turns 31. In 3 years, Cooper seems almost sure to be superior.
You also don't just pay players under contract "free money" to keep them happy. What kind of message does that send? You don't pay elite players like Mack, but shell out money to the WR who makes headlines for being egotistical? Khalil Mack is by no means terribly inconsistent - he had just 4 games without a sack. That's rather consistent if you ask me. There isn't a single DE in the league that gets a sack every single week.