Yeah I think I read that analytics favor Gasol by a significant margin. He is better defensively, a better passer, and spreads the floor more. A lineup with Siakam/Gasol up front is going to be an upgrade. Enough of an upgrade to win the EC? I don't know. They couldn't really realistically improve at SG, SF, and PF, and Lowry is probably untradeable with his contract, so the only other option was to upgrade C, and they did.
The way the roster is set up, Masai is preparing for a rebuild after this year. This is basically his AA-2015 push except he actually cares enough to maintain flexibility, whereas AA threw both his middle fingers up and knew he was gone anyway.