BW comes the closest structurally with the endgame loop going into the Elite 4 rematch and actually becoming champion, even if it's far less than what even GS was doing and the optional boss battles are significantly disconnected from most of it. DP and SM are just kind of maps around the Battle Tower clone and RS and XY don't even fucking try. As for most content in a more general sense, something like Emerald or B2W2 are probably the best options as there's only a little overlap with what HGSS provide, but neither of those games have the campaign-like content that HGSS offers (B2W2 has some BW maps recontextualized but there's not a compelling reason to visit them unfortunately). HGSS is probably the best whole package unfortunately, so you've arguably hit the peak unless you really like something else about the Gen 5 titles or something in Gen 7 really speak to you. Like you don't strike me as somebody who would enjoy ORAS's connectivity features where half of them don't work because 3DS online is dead, let alone XY or Sword/Shield's nothing.
