Let's look at 3 factors:
1) Potential role on the Kings
2) Salary Cap
3) Assets given up to acquire player
1) He is not beating out DD or Voynov as a PMD on the first two D pairs. Hence, he is by definition a 3rd pairing guy. Is he substantially better than AMart, or would AMart beat him out? AMart has the benefit of being in the Kings system for a couple of years and understanding what is required. If MDZ can't play defense, he's not playing for Sutter, that's for sure. When Greener comes back, can you assure that Sutter won't bench Amart / MDZ? Thus MDZ would potentially be a #7 D.
2) AMart cost $1.1MM in cap space, MDZ $2.5MM
3) MDZ is not coming for free. We would need to give up assets. What assets do you propose to give up? Would we be a better team (by subtracting AMart, and adding MDZ.) Further, what assets are you willing to give up for a guy who is potentially sitting on the bench behind Mitchell / Green?
Finally, MDZ is not a 35 pt player on the Kings. With the Rangers, he is the only offensive D-man they have. He received #1 PP minutes. He may not play any PP minutes for the Kings since we have DD, Voynov, and Muzzin and Richards/Stoll.