Not to be a farseer or anything, but i would understand that point of view if we did not know what story Undermine will tell. There is room for the dark heart to mean a lot, for it to be a major story point and for a new antagonistic force be presented in this patch.
But that does not seem like the case.
Gallywix comes out of nowhere, so as an antagnist, he does not smooth as the big bad of this patch.
The dark heart has not been the focus of the expansion so far, only really being focused on in the last cinematic of the 10.0 patch, so if you remove that patch, it would not even seem that important.
Furthermore, we know that the heart is gonna get fixed this patch about midway through the story and the rest of the story is about taking down Gallywix.
The Etherals do have a role in the patch, but story does not seem to explore them much, only using them as the lackeys, that gets the heart before we do. Does not really set much up for them being the new bad or explore a big new character. I think the main etheral person is just called "nexus-thief" or something
So yeah, i still feel like this patch was planned to just be put in whenever, and then they sprinkled some random story stuff here and there to make it fit with TWW.