The stats may be slightly different but I do believe diamond Durant plays better than sapphire. Diamond KD is probably my favorite player on my team, because once he's on fire he is unstoppable.
The main reason for wanting a diamond player is the fact they are rare and usually the best version of that player. Also the appearance of the card, who doesn't like diamond? I understand how people get upset about not getting him but if everyone that wanted him got him, then the card wouldn't be rare.
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I'm happy I no longer have to worry about kobe or kd, they are nearly impossible to grab now.