In D&D terms, a kobold should just be a kobold. It would be very odd if all kobolds were eventually level 20 and wielded awesome magical weapons just because you did.
In D&D terms, if you are hired to kill a kobold and wait a few years while you deliver flowers and such you'd expect to end up fighting a lot more than just one kobold.
Also, what's the point of growing more powerful if everything grows powerful with you? We saw how that worked in Oblivion where there was a disincentive to leveling.
The point is to make non-linear games with optional side quests possible: if you have multiple quests that can be done in any order then the player will end up either getting bored or getting curb stomped unless they do the quests in the exact right order, so throw that idea out of the window.
You also can't have optional quests that give xp or equipment - you'll either end up being too powerful, making the rest of the game boring or the game might be balanced to require you to do most of the supposedly optional tasks to stand a chance in the fight.
Oblivion might have been a bad implementation of this idea, but in general the alternative to having enemies scale to the player's level are much worse.
Oblivion and Bethesda do not do things the same way. Using a Bethesda game as an example nullifies your example. It is better to use DA games and ME games as one instead. One thing a lot of us, myself included wanted from DAI was that enemies come back, repopulate and don't stay dead. The single biggest flaw with the previous DA games revolved around that you have NOTHING to do really after you have completed the quests and gone through each area. Enemies would be dead for good.
No offense, but you should just go back to playing Skyrim. There is nothing wrong with wanting an open world open ended bear killing sandbox, but let's not turn all games into bear killing sandboxes. It is OK to have games that actually have an ending.