Right and I agree with you there. Both are appealing to me. But I don't see Skyrim or any TES game being given that qualitative difference, so though my suggestions may seem like grinding to you, because ultimately we'll get the same results, mine just took longer, its the only way I can see of giving the game something more, for those of us that want the extra challenge.
Bethesda aren't going to change the game in that regard, I'm fairly certain of it.
But heck... it is possible someone might be able to mod the game to add different modes of play eventually.
And putting aside the word "challenge" for now (it leaves a bad taste in my mouth)... Why don't you just play the game differently? Obviously some aspects of the game aren't giving you satisfaction, so it stands to reason that you should try to make do without them. Change the way you play. Surely that would resolve the issue completely?
Heck, among the stranger things I've done in the past (that might make me seem like a hypocrite)..... I used to really love Pokémon Red. Used to know the game inside out. Got tired of replaying it normally, so one day I started playing the game with the Gameboy held upside-down. And when I completed it like that, I did an entire playthrough of Pokémon Red in the dark... by sound alone. Even I think in hindsight that was a bit of a silly waste of time... but still.
Then I went and completed Pokémon Gold in Japanese... before it was out in English. Heh... crazy times.
It's fairly simple. Currently, for dragons and other enemies, when they level up they are simply given a boat load more health and that's it. So, regardless of what difficulty you are on, if your sword does 500 damage, you still do 500 damage to said enemy. You basically negate their armor (if they even have any).
A way to put a stop to this is to boost their armor so that, on harder enemies or harder difficulties, your 500 damage sword now does... say 350-450 damage, depending on the enemy.
This does not make fights last forever, it does however make the enemy actually tougher rather than just having an ocean (instead of a lake) of Health.
No extra content needed. No extra grinding needed.
So instead of hitting it once or twice and it is dead.... you have to hit it 3 or 4 times and it is dead? Aside from the fact that the difference is relatively minimal, it is STILL grind of sorts. It is still achieving the same result but taking a little bit longer to do it at no extra gain. Where is the satisfaction in that?
Personally, I'd rather have dragons that use different Thu'ums but the same health than dragons having to be hit more before they die.