>>51013396The new pokemon thing may seem big, but remember that out of all the games directed by Masuda (RS, DP, BW, XY), BW is the clear outlier there. The other three heavily use old pokemon in their regions. I'm not sure how the Japanese reacted to the BW dex, but if it didn't go well there, then that might explain why they didn't do it again.
I think the postgame part is a bit disingenuous too. XY actually has more routes, but it made use of them before the game was over. I don't think it's fair to say that it was all the same amount of effort in both, just sectioned differently. And I'd agree with the rivals comment, the BW ones were more relevant to the story at large, while the XY ones were more designed as shounen tropes to represent bonds and friendships as per its theme, but it was kind of hit or miss.