This in itself is one of the culprits of reduced levelling speed - since enemies will eventually die incredibly quickly. Where normally you'd be able to get in quite a few spells, melee attacks, armour damage, blocks and such which would usually give quite a bit of skill experience, you're left one-shotting everything and gaining next to no experience without increasing the difficulty.
This is true. But I also don't see this as a bad feature (although I don't mean to suggest that you thought otherwise). Once the enemies stop becoming stronger, there's less incentive to increase the strength of your character. Indeed, there's a
disincentive, since as your character becomes much stronger relative to the enemies, the decreasing difficulty hurts the enjoyment of the game.
Of course, there are reasons to want to continue leveling up. One is just to max out your stats. But there are slightly more (dare I say it) tasteful reasons. You might want to change your character around from (say) a warrior to a mage, and you need the level ups to get the perks.
The problem also, is this; If you focus much on a non combat skill, you will have a much harder time handling the enemies you're facing. I would have loved for some skills to not add to the actual character level, such as lockpicking and speech.
Again, this doesn't strike me as an altogether bad feature. Non-combat characters
should be weak in combat. Of course, the leveling does screw this up a bit, because as you try to beef up your combat skills, the enemies keep getting stronger. So you'll always be a little behind the enemy strength, at least until you've reached higher levels. But I don't regard it as a major flaw.
Having non-combat skills not count runs into difficulties, I think. For instance, having a high lockpicking gives you easier access to loot, and so more money. This allows you to buy better gear and followers, which increases your combat strength. Similarly, having a high speech allows you to buy better gear for less gold, which increases your combat strength. If lockpicking and speech don't contribute to
enemy level, then you can exploit this to make your character much stronger than the enemy (simultaneously improving non-combat and combat skills will make your character very strong). If lockpicking and speech don't contribute to
your level, then when do you get perks for those skills? If it's just when the skill is high enough, can you use the perks for other skills?