The meta is, and always has been, conquest and not raiding. Conquering pops gets you all the pops, gets you the base growth of a new planet, and gets you the buildings and districts to employ the conquered pops without having to spend anything yourself. Not to mention it gets you the territory, starbases, and resources of the conquered empire. Raiding might get you more pops over a very long period of time, but it doesn't win you the game. Conquering wins you the game much faster.
If you're leaving an empire stripped of pops so you can do it again ten years later, it's much better to just conquer that empire and instead of waiting ten years conquer a second empire instead. Then another, and another, until there aren't any left.