Hmmmm. At first glance I think this is a fine deal for both sides.
There is no way I'd pay a 5'9" 29 year old, who might have a hip issue, $30M-40M/yr. Kyrie also fits the Celtics age group better and he'll still be in his prime once Tatum and Brown are entering theirs. Of course the Celtics will need to get him signed long-term for that to matter.
For the Cavs, they can still compete next season and could get a very good young player to build around with that Nets pick. Crowder should also still have decent value next summer if they want to flip him elsewhere if LeBron leaves.