I think Fisher did a solid job his 2nd season but ultimately Phil wanted someone more innovative on offense. The offense had become to wane under Fish and Porzingis began to play worse.
Hornachek is a much better coach on offense and is utilizing Porzingis far better. If you see the one game that KP was ignored this season, Jeff was all over the team. I think this is where Phil sees value in Hornachek. He's a better basketball mind on offense, gets more out of KP, and also has more "zen" qualities.
The downside in Hornachek is his teams don't defend all that well. Or he doesn't seem to value that end much. You look at his Suns teams even, they weren't that good on defense. He clearly needs someone better than Rambis to help him.
I was surprised Fish got the boot, but I think Hornachek is a much much much better coach for offense for KP. To me in the longrun that's all that matters. If these years we are a 30-35 win team while Porzingis keeps developing, you want a coach for him who will allow him to truly maximize his potential. Too many times last year I saw KP get the bench as soon as he missed a shot or two or tried to be a little creative. This is a vital factor in the coaching upgrade.
Our team outside of KP is old, on their way down (core starting 5). They play like it. No consistency, not enough energy on defense. I've gone from being extremely excited about this season to just hoping we can stay close to .500 and keep getting KP to grow on offense. As we saw in this 1st half already, KP has a monster in him that can be unleashed with time. Some of his moves are already incredible. When he hits his prime, we need to make sure we have a prime star guard next to him. If we do, we're set.