I don't think Cohen did anything wrong. It's a business, players use different tactics all the time to gain an advantage in negotiations why can't the owners.
Cohen might be also protecting the team and himself from fan outrage. Usually if a player doesn't sign an extension the fans blame the team, which could hurt attendance/revenue. Him coming out and announcing the offer shows that they were willing to give him more than a fair offer. The owners priority is to protect the team, which is what he did. Do you think if the team low balled Lindor, his agent or Lindor himself wouldn't have leaked that info?
As for this effecting future free agents, I think this will have very little play on that. The players will still go where the money is.