I generally saw the half-elves niche as similar to the Dunedain or Numenoreans or even Atlanteans. They were not as long-lived as elves, but they lived longer than ordinary men. Similarly, in Tolkien's view of things, they were often more charismatic than either regular humans or even some elves, usually Noldor precluded there.
WotC's change regarding half-elves also seems a bit at odds with the identity of the Khoravar (half-elves) in Eberron, who saw their own identity as not half-elves or half-humans per se but as the distinct children of Khorvaire, with both elves and humans being migrants to the continent of Khorvaire from Xen'drik and Sarlona, respectively. The whole idea of mixed heritages like the Khoravar having to choose either elf or human as their species kind of flies in the face of that narrative of having a separate and distinct identity from either elf or human.