The OP clearly knows how to defeat the game. A shadow warrior assassin is the hardest hitting class you can make. I have one and I can testify to the ability to one shot nearly every creature in the game including bosses. It is extremely overpowered even without exploiting enchanting which I did not do. However if I do desire a challenge with that character I can have that challenge. It would just require me to balance things out between the games difficulty and the gear and abilities I possess, mostly the gear. While this may not seem ideal it allows a greater deal of freedom in the game than simply artificially scaling it to the player or having a difficulty so hard that fights become tedious. They tried scaling with Oblivion but players hated it. They put in some really difficult creatures in a Fallout 3 expansion but players complained about those as well. It seems there's no way they can make everyone happy. That's why I suggest tuning the character back a bit and learn to work within the games current parameters. It's obvious there won't be an overnight change to the difficulty levels in Skyrim. For now we have no other solution than to make it work with what we have been given. That doesn't seem to difficult to understand.
Everything you have said points exactly to the problem we are critisizing.
Bethesda doesn't know how to balance a single player game. That's why we're critisizing it. We shouldn't have to change how
we play so the game can keep up with us, we're supposed to change how we play so we can keep up with the game.
"We have no other solution other than to work with what we have been given."
Yes, that's the problem we're trying to get fixed and rebalanced, so that there's no problem in the first place. Again, we shouldn't have to scale ourselves so that the game can keep up, we should be scaling to the difficulty of the game so we can keep up with it.
We buy better equipment, perks, etc so we can defeat tougher opponents, we as the players shouldn't be then negating that so the CPU has a chance against us.
Some enemies should be various set levels, spread out in various areas of the game and spawned when the player reaches certain levels.
Some enemies should be scaled to the player at all times and placed above the player level.
Some enemies also need to be exactly level with the player at all times.
And some enemies, and dungeons, should have new ways to add difficulty to the game other than just an ocean of Health, or limitless Magicka, etc.
The concept of "because it currently is the way it is, we have to gimp ourselves for a challenge" is not a hard concept to follow, it is however a concept that should never happen in the first place if the game was properly balanced.