I thought the biggest complaint was that "Oblivion was worse then morrowind."?
I think that's the generalized version of the same complaint. I'll take back the "biggest," and change it to "one of the biggest." Okay?
You ever tried running away? Really, just because you encounter something doesn't mean you have to kill it.
If it's the Main Quest, and you run away from dealing with Kvatch at level 5, I guarantee that it will not be easier at level 25. The PC may be able to breeze through it, but if your objective is to keep the Kvatch Guard alive, it will be very difficult. They level to a certain extent, but they have light chainmail armor and steel or silver weapons. The enemy is going to go from a handful of scamps to high-level atronachs and dremoras with multiple damage spells and Reflect. And there are more of them as you level up. There simply aren't enough of the guard to manage, with their poor equipment.
The same thing happens later in the MQ. It's much harder to keep your allies alive.
It's not a question of "difficulty" exactly. The problem is that the way enemies are scaled in both equipment and skills leads to a greater and greater imbalance as the PC levels up.
Since, by default, creatures are always a set level higher then the player, there is minimal gain in difficulty by leveling. The only real purpose to leveling is to aquire different aesthetic armor, and fight different monsters.
This would be true if the "different monsters" didn't have increasingly difficult-to-counter attacks. They're not only higher level; they also have more varied skills, more different kinds of attack, and much better equipment.
I'm not actually complaining about this. I happen to like the increasing challenge, but I don't think it does anybody any good to pretend that the so-called "Leveling Problem," linked to in the wiki above, is non-existent.