I mean I been playing the series since 4, so I'm not a scrub. This is what I am gathering. I am only playing him as I refuse to play the ninjas. I wanted Zack, but TN gave me the nope face. Matt told me he wasn't in and thought he was trolling.
Both paly Stun launch. Both do massive damage on CH and HCH but solid NH damage. Their best attacks are either high or mid and lots of string that are high mid and mid high. This is Mexican Zack without stances. They are very similar.
Zack is not a stun launch character, he can stun launch you but that's not where he thrives. those two play nothing alike, if anything, Diego is going to bait you to hold because of his high throw damage.
His combo damage is really good. You can use the throws for punish. Also someone like Bass and Tina will do that. Well Zack does need a number of stuns to get his damage but Diego does the same too. You have to do like two or three stuns before you get the stun. Keep in mind this jsut my opinion. I'm sorry, but he really feels like Zack. I don't see why you would bait holds when he does such good raw damage.
6p is more than enough to launch into 9k for a juggle. It only whiffs on Hayate and Diego it seems, which you just use 8k and it launches high enough. You don't have to play the stun game at all with anyone. Everyone launches the same height.
Granted I don't really play Zack much, but I'm really not seeing any similarity.