We didn't need Pokemon Z, specifically. What we needed was proper closure of the story - and I use that term very loosely, because this is Pokemon we're talking about here - that the games had with Mega Evolution etc., which they attempted to provide with the Delta Episode in ORAS. It wasn't perfect, by any means. But it was an attempt. There was at least an acknowledgement there that things were left unfinished, and some effort to tidy them up. What we really needed was for the Delta Episode to be better.
But I am going to stubbornly insist that we did not need to tread through Kalos a second time just to have the same plot told to us yet again only with Zygarde as the cover star this time. Which is exactly what Z would have been. Third versions typically DO provide more content than the base versions, I will agree - Emerald was better than Ruby and Sapphire (and ORAS, for that matter) and Platinum was better than Diamond and Pearl - but given the timing of the games and the fact that these were the first games on the 3DS and were built completely differently, Gen VI was only ever going to be a stopgap generation. That was only made even more apparent when Sun and Moon were released.
I mean, look at the difference visually, between Sun and Moon, and X and Y. It's clear which one of them had more effort put into it - XY look and feel like a trial run, and it would have taken a lot more than a third version to change that. Creating Pokemon Z with SM visuals would have likely required making Kalos again from the ground up, and would have begged the question of why the hell they didn't do that in the first place...and it really wouldn't have been worth it for a little extra content, would it? Kalos was rushed, plain and simple.
Kalos was an under-developed, largely unexplored region. But the flaw was in the design of the region itself, not from the lack of a more complete third version, which would have had the same flaws, just with a different Legendary on the front cover and a little extra content. In a series as similar as Pokemon, these little things often make all the difference, but in this case I don't think it would have, especially looking at Sun and Moon.
I didn't like Gen VII at all, but even I can see more effort was put into designing Alola than Kalos. I wouldn't say Sun and Moon need a third version, and they're in exactly the same place as XY are right now, only because more effort has been put into it, they're generally regarded as more satisfactory titles. Given the huge list of flaws with XY, it would take more than a third version to salvage Kalos as a region. What we needed was for XY to be better as they were. What we needed was for XY to have Sun and Moon's visuals, have more effort put into making them a more complete experience, or for a greater sense of closure provided with the Delta Episode in ORAS, which could have tied into XY more than they did.
Gen VI was just a mess. Wishing for more wouldn't have changed that, in my opinion.
