I played part of Oblivion once with a mod that set static enemy levels, making certain areas inaccessible until I got better, because I didn't like that I could never grow stronger than any of my enemies. But it did lose something of its open world flavour, level-gating much of the content. And that's okay, there's nothing wrong with level-gating as a design choice, as you pointed out it's exactly what World of Warcraft does. But Oblivion's design choice seems to be to allow the player to go anywhere at any time, entering any dungeon at will and being able to find a level-appropriate challenge there, as opposed to gating the content and only opening up certain areas as you reach certain levels.

And to be honest, I think there's merit to that choice. If you had set enemy levels, how would you properly balance a game like Skyrim? Would you expect the player to advance through all the story quests first, and build the level curve to match that? If so, what happens when they go do a bunch of side-quests for the Thieves Guild and the Mage Guild, grow four levels above the main story content, and then find the rest of the main story to be incredibly easy?

I think that level scaling is an appropriate method of providing consistent challenge for the player in a world where you can choose where you want to go and what you want to do. It wouldn't be such a good choice for a game like World of Warcraft, because they are different games. But by the same token I don't think WoW's system would work as well for Skyrim.

I think that setting the dungeons in Skyrim to scale with your level is a wise decision, because you will always be challenged by them, and I think that locking the levels once you enter so that you can level up if you want is also a good way to go. But I would also like to see a different system in the main open world, so that you aren't always fighting challenging monsters as you walk through the woods. That's why I like my min/max enemy level idea for the world map enemies.

You could level-gate certain areas in Skyrim so that you have to be sufficiently advanced to enter them, but at that point you are in some ways forcing the player to advance in a certain way, and that's not what Elder Scrolls games want to do. And if every world area is level-gated, then you've just created a zone system that the player has to advance through in a certain order, whether there are physical boundaries or not, and that's also not what Elder Scrolls wants to do. I don't think that's necessarily a bad thing.