He gets a lot of crap, but his last 3 year averages are
22.7 points, 39.5% from 3, 2.4 blocks a game
20.4 points, 35.2% from 3, 2.0 blocks a game
20.7 points, 37% from 3, 1.5 blocks a game
I do not know of many 7 foot or bigger guys that have those kind of numbers in the league, to be able to give you 20 a game, 2 to 3 three pointers a game (floor spacing), rim protection, and of course some shot creating in the post.
And since Dallas has traded for Porzingis, they have been a playoff level team. I mean, not like they would be a playoff team with the likes of Wes Matthews, DeAndre, a late first round pick and Dennis Smith Jr. The Knicks got robbed, none of those players are even with the team right now.
His main issue is that he misses 30% of his games. This will always be an issue with him, and part of why Phil Jackson wanted to sell high. You can not be a teams best player and miss those many games. In Dallas he is their second best player and it works well. This season the slow start was due to the injury in the offseason and not being able to work out. Now that he is rounding into shape, he is playing very well again. Dallas has been a better team with him. If Dallas trades him, they will get much more than the Knicks ever did, and that is the reason they would make a move like that, they would be upgrading in assets. The Knicks have not utilized their assets at well. They could have signed Randle, and had Porzingis as well. The guy was never going to give up a 5 year max extension to take a 1 year qualifying offer. Imagine having Thibs defensive coaching and 2 all-star level front court players like KP and Julius. You eventually trade for an elite guard-wing, and now you are an East contender for years. Yes, they had the space to do both. Sign Randle, and as well as extend Porzingis using his bird rights.