Did people forgot of decades of darkness by jared? They fullify the challenged but different as netherlands got rhineland parts and joined in 1848. But still count
This is a good example, as Jared sort of played a trick here by having the "Netherlands" include some genuine German territory, as well as francophone Wallonia, with the whole area being inherently tied to that rather egotistic William I. The ATL German Confederation proved integral to maintaining his rule, leading to a slow drift into the German world+some unifying wars+the massive material benefits the Netherlands accrued+the very strong federal nature of Germany allowing for local identities and interests to be largely fulfilled. The DEI remained very much tied to Dutch interests even as part of a broader German Empire. Even after a century of being involved in "Germany" the Netherlands retains its own identity, but with that century having been so fruitful that identity has become tied to broader participation in Germany.
The key for getting the Netherlands into Germany is not to make the Netherlands more German, but to make "Germany" a more pluralistic society that allows for local identities and interests to be pursued in conjunction with the more civic German identity, not in spite of it. The OTL Kaiserreich was never going to be this state, but it's a failure of imagination to say that a German state could not emerge in the 19th century that could successfully include nearby minorities like the Dutch, or for that matter Czechs or even Poles.