The Magic seem ready to make a playoff push. They have a very strong core in place, and need to supplement them with the right role players. Here they acquire THJ, who can be a great floor spacer for them, shooting a very good percentage at a high volume (over the last 25 games he shot over 45% from nearly 8 attempts per game). He would be a great fit next to some of the guys who aren't as great shooters, like Fultz, Banchero, and Suggs. The Magic also acquire a future pick swap, which could be very valuable if Luka asks out.
For the Mavs, they take a huge risk here on Isaac. If he is healthy, he is a perfect compliment to Luka, bringing incredibly length, defense, 3pt shooting potential, and versatility. However that "if" is doing some heavy lifting. His career has been completely derailed up to this point. However if it works out it would be huge for them. Okeke provides some size as well, and another upside shot at the wing. Hardy and Green will help absorb the loss of THJ, but this would make the Mavs much more balanced.