What does it matter whether the three "sub-races" are presented as races or sub-races? Who cares? The 4e lore, including the sundering of the elves, is classic D&D seen through the prism of the Dawn War and the Feywild. I have a drow PC in my 4e game, whose goal for the whole campaign has been to kill Lolth and undo the sundering of the elves. The player of this PC has never played D&D prior to 4e, but has not had any trouble understanding the interrelationship of the three varieties of elf.
What does it matter?
Well, it doesn't really for the drow. Not really. And honestly it wouldn't have mattered if they had presented a race of elves with two subraces
or a race of wood elves and a race of high elves. That's all semantics.
The problem is solely that they decided to remove the race/subrace of grey/high/silvanesti/sithican/sun elves and replace them fae from another dimension that can teleport a hundred times a day and are the source of all other elves. They needed the smallest of small tweaks to "fix" the problem and instead redesigned it from the ground up.
There's so many things wrong with that. The flashy racial power, the retconning, the recycling of an existing name, the mandating of the feywild. And while it arguably "fixed" the problem of differentiating between Nerath's high and wood elves it just created more problems in other worlds, most notably the sweeping hand waving necessitated by the Forgotten Realms. But other worlds would have been just as bad: Silvanesti in Dragonlance and Sithican elves in Ravenloft were both grey elves but very much not faeires tied to another plane, and teleporting was not a fitting racial power. There were frequent discussions about what to do with eladrin in those worlds, and how to handle wizard elves. So eladrin did not make it easy to update 4e in those worlds, nor did it solve the wizard/ranger elf split (and arguably made things worse). Of course, just using elves was unsatisfying as the race was unsuited for being a wizard (pre-Essentials).
If eladrin didn't teleport but had some simple magical ability, then things would be less problematic, as the extradimensional fluff could be ignored and just the racial mechanics uses. Or if the eladrin power was subtler allowing it to be reflavoured as less overt magic. But they teleport every 5 minutes... that's huge. That just doesn't work with existing lore or the thousands of novels. (If all sun elves are eladrin and can teleport there are probably dozens of instances in the Forgotten Realms novels where being able to teleport would have been handy.)
The eladrin were simply a bad fix for the problem. It was a fix that made more work than leaving things alone.
Now, again, this does not make the race itself bad; in a new world they work just fine. It just makes them a poor substitution for high elves. And saying the eladrin fix was poorly executed is not edition warring. The fix would have been equally bad in any edition. I like 3e but I can criticize the execution of 3e elves as well and burying of the wizard elf variant in the DMG was a mistake.
This is simply a critique of the purpose and execution of eladrins as a concept.