I’m not going to sugarcoat this. Kemba Walker is younger than Al Horford and at this stage in their careers, he’s a better player ...when healthy. In essence, the Celtics sent out the best player in this deal and had to add a first rounder to get it done. That’s not ideal.
However, it may just have been the right deal to make. In particular since (due to his health and salary) it seemed like some kind of deal was destined to happen. The team needed a shakeup and the Celtics wasted no time doing the shaking.