Well, on GOG you do indeed have a "Divine Edition", which includes all the digital extras that we have paid for and that were promised us during the KS campaign (and that's the one I was talking about... if you have the Kickstarter CE, then you should have those digital extras on GOG as well - the same ones you currently have on larianvault - if you don't have them on GOG, you can get them added with the help of GOG support).
And there is the "Eternal Edition" (I assume that's the 'top tier' one you're talking about) that, in addition to DOS2 and its digital extras (same as in the Divine Edition), also includes all the previous games in the Divinity series, with their digital extras. If you already own those previous games on GOG, then you should also already have all those digital extras (assuming you have the CE version of the DOS EE, otherwise you'll lack the DOS EE CE bonus content). So as far as I can tell, there's nothing unique in the Eternal Edition that would require purchasing it !?!
I took another look after you posted this and you are correct....at least now you are. But it looks to me like the contents of the editions were edited after launch. Stuff like the soundtrack and at least one of the art-books were initially exclusive to the Eternal Edition. So it seems they quietly fixed things behind the scenes and just never said a word of any of this....hoping nobody noticed I imagine. The fact that it even came to this still leaves me more than a bit upset.