No? If I'm reading you correctly and you're saying that good postgames were an outlier in Gen 4 of all things I'm going to assume you're trolling.
Gen 4 was the last generation with consistently good postgames, yes. Even the lacking Diamond/Pearl postgame wasn't that bad compared to what little you got later on.
Even then, Gen 1 didn't have a postgame outside of one dungeon, Gen 2 let you explore Kanto again but outside of gym leaders it was mostly barren due to lack of cartridge space. Emerald had a good postgame and Sevii Islands were a nice distraction in FRLG, but there really isn't anything to do in RS outside of Battle Tower. Hell, the GC titles had the best postgame that generation and those weren't even done by Gamefreak, you could argue these were the original post game episodes that would get popularized later on.
So yeah, Gen 4 having consistently good postgame was an outlier since the franchise wasn't ever really known for it, before or after Gen 4. You know, unless you really got into the competitive facilities these games had, in which case we're wrapping around that whole argument again.
B/W prioritizes adding things to the benefit of competitive autists over having a decent postgame, are the games that receive then-unprecedented criticism, and Gamefreak backpedals so hard we got BW2. Again, you're restating my point; catering to hypercompetitive autists was a deliberate choice and came at the expense of stripping down the singleplayer experience.
Their priorities in singleplayer changed for a more cinematic experience with "deeper" stories and characters(ie your "friends" and gym leaders being involved in the main story) at the cost of lower difficulty and less gameplay. Competitive has nothing to do with this drop in quality, what it shows that the people responsible for gameplay mechanics and balance were the only people at Gamefreak who still knew what they were doing. That is, until they got lazy or the company changed direction during the end of Gen 7.
That postgame sucked. All the rocket grunts were piss easy and only had ONE pokemon on their team. Only the bosses had some sort of challenge but only because they were using legendaries.
in fact that was one of my issues with Gen7. Every trainer battle only consisted of 1 or 2 pokemon. Even Gen6 did this with the gym leaders and they were underwhelming... no other new pokemon on their teams even in the Chateau Writ battles, just the same two mons just higher levels.
Like I said, RR was planned to be part of the main story but was scrapped. I guess they needed something to quickly throw into the game to make "ULTRA CHANGES" worth the 40$ so they decided to throw in the tech demo they had lying around as an easter egg. That's why the teams are so lame and so is everything else, they had nothing made other than models and boss fights for that dungeon. I guess they figured all the member berries would carry that moment, altho I do appreciate that you can set the theme of your Festival Plaza to Rainbow Rocket(along with their theme) once you defeat them.