I suppose that you could argue that elf eco-specialisation represents a hint that not only are individual elves long-lived, but that their species is also extremely venerable. If individual elves live a few thousand years, there is still sufficient time for eco-specialisation if elves have been around a few 100 million years.
Or alternatively, that elf eco-specialisation is not due to evolution via errors in differential reproduction, but is the result of deliberate (or accidental) elf-engineering by magic/science at some point in the past.
You could make that argument, but for dwarves and gnomes as well? Against a backdrop of comparatively little speciation in the “mayfly” races?
My gut feeling is that, if asked, the game designers’ response would be that the elves actively used magic to help them adapt.
But magic like that is kind of out of character for dwarves & gnomes. Sooooo...divine intervention?
Which just begs the question of why the gods of the orcs, goblins, etc., didn’t intervene on behalf of their “children”. Especially when we have creation stories of how Gruumsh reacted about orcs being cheated...