Are you ignoring the part where he talks about b/w? Compared to all the other games BW easily had the most content.
- side quests with the baker and waitress where you get a part-time job
- dream world
- Finding the seven sages
- extra hidden areas you can find with HM's
- The ghost girl/Zoroark
- Train Station
- black city, white forest
- that poke movie place
I'm probably missing some more things, I haven't played BW for quite a few years. Heck it's charming to revisit these games and do little things like play around with the music in the towns.
Honestly is there any pokemon game other than BW that you can do this much exploring post-game? I know S/M had little side quests with npcs and collecting stickers/badges but there was hardly any "secret" routes and no hidden dungeons.