Aside from the math working out to allow the Cs to sign Hayward and Yabu this trade is perfect in one other sense.
It gives the Cs a potential rotation to match the Cavs in a 7 game series. I view the addition of Morris as an upgrade from JJ. Both players are 4/3s who shoot the 3, defend the perimeter well and give a level of toughness. Morris bests JJ is all these areas. Where this will help the Cs the most is vs the Cavs when they go with their smaller lebron and 4 shooter lineups. Where last year the Cs would match Irving,Smith, Jefferson/Korver, Lebron and Love with IT,AB,Smart,Jae and Al and would give up size at every position except AL. This year will be much different. Now the Cs can go with IT/Smart, Hayward, Crowder, Morris and Al giving them equal or greater size at each position. Couple that with the potential improvement of Brown and the Cs have really improved their chances to reach the finals.
The growth and development of Brown and Tatum may even see the Celts go with one of those players late in the game in place of Crowder. Where Jae is primarily a 3-D player who isn't going to exploit the Korver/Jefferson match up both of the young wings could have the ability to exploit that match up in the Cs favor.