There's no game mechanic I despise more than level scaling. I also question the mindset behind it -- that any game, open-world RPG or not, should have a relatively constant difficulty throughout the entire game (never too easy, never too hard).
Super Mario Analogy
Let's consider the idea that a game which doesn't have a relatively constant difficulty throughout is broken and in need of a fix. In that case, Super Mario Bros. is fundamentally broken. In all SMB games starting with the first on Famicom/NES, the first stage was always exponentially easier than the final stage in which you fight Bowser and save Princess Toadstool.
So if we apply this level scaling mindset that the challenge of the game should be relatively constant throughout, the first stage should not be considerably easier than the final stage of the game. Experienced players who have poured hours into the game should not have much easier of a time completing stage one as opposed to completing the final stage of the game.
Would that make a superior game? Perhaps some people consider this analogy unfair since SMB is mainly a linear game.
Grand Theft Auto Analogy
So let's turn to GTA games. I've found in GTA that if I steal the fastest cars, possess the heaviest body armor and an arsenal of weaponry including heavy assault rifles, every part of the game becomes considerably easier. Some missions even become a total and relaxing breeze with such a powerful character. So from the level scaling mindset, the game is fundamentally broken and in need of a fix.
If we apply a level scaling mindset, then there are simple things we can do to make the game consistently challenging no matter how powerful your character becomes. If he has an assault rifle and heavy body armor, we can make all the armed pedestrians, thugs, and cops also have heavy body armor and assault rifles. If you only possess a pistol and no armor, so too will all enemies in the game. Voila -- now the game is no more challenging if you only have a t-shirt and a pistol than if you have assault rifles and heavy body armor.
For speed missions where you need to get from point A to point B in a limited amount of time, having a super fast sporty car obviously makes such missions considerably easier than if you were to try to complete them in a golf cart. So we can apply a level scaling mindset there and make it so that the distance from point A to point B increases or the time in which you are allowed to complete the mission decreases based on how fast your car is. Voila -- now the mission is equally difficult whether you're driving a golf cart or the fastest sports car in the entire game.
Would that make a superior game?
In open-world RPGs, does it make sense to be able to dispatch a dragon at level 1 while being slaughtered by a couple of common thugs on a well-traveled road 20 level ups later? Is it really that fun to try to have a relatively constant level of challenge throughout the entire game?
Granted it does allow you to explore a heavily-armed fortress at level 1 without it being a suicide mission and likewise find yourself dying on a common road at level 50 with elite gear to petty thugs, but is it really so fun for no part of the game to ever be too easy or too hard?
I remember playing Ultima 7 as a child. I started off at level 1 and, knowing I was doing something really dangerous, I traveled off the beaten path from Britain to Trinsic and to the south of Spirit Wood, always paranoid about any sort of enemy I could encounter at which point I was ready to run for my life given that my party members were inexperienced, ill-equipped, and could barely swing a sword. And along the mountainside, I encountered a cave. I ventured into it only to find I stumbled into a dragon's lair with eggs surrounding me. Pumped full of adrenaline, I tried to carefully explore the area for valuable loot until I encountered the mother dragon who obliterated my entire party before I barely knew what hit me.
That was fun! It was fun to be vulnerable and weak and exploring areas I knew to be risky and out of my league. I then reloaded a previous save and decided to avoid venturing again into that dragon's lair until much later in the game. I revisited it far later after my party was battle-hardened and well-equipped and managed to slay that mother dragon which previously obliterated my party long ago, and that too was really fun!
I cannot imagine the game ever being so gratifying at both low and high levels if venturing off the beaten path was not so treacherous and borderline suicide at level 1 or if I still could not have more confidently done so at level 20. The fact that the game didn't offer a constant challenge and had parts too difficult at low levels and parts too easy at high levels was what made that open world so rich and treacherous to explore.
And it wasn't like the fact that certain parts of the world were considerably more difficult for lower levels than others reduced the game to a linear adventure. There were always infinite ways in which I could rearrange the order in which I traveled to areas. The difficult areas were those always off the beaten path where weary travelers would never venture to go, but most of the massive map could be explored by traveling along safe routes. That, to me, is an open world RPG done right, and level scaling would only detract from all those elements that had me so excited and nervous at lower levels and increasingly confident to explore deeper and off the beaten path at higher levels.
Anyway, I hate level scaling. I'm aware of many of the arguments that it takes away any incentive to grind since it doesn't really help make the game any easier. Well, in that case, I'm back to the Grand Theft Auto analogy where a similar argument could be made that there shouldn't be any difficulty-related incentives to hoard the heaviest weapons, armor, and fastest cars. A game should not seek to constantly scale the difficulty according to the power of your character as far as I see it. Such kills the joy of becoming more powerful in the first place.
Personally I liked how Open World RPGs from long ago simply avoided level scaling, allowing many parts of the game to become a breeze if you became a powerful enough character with only a few parts left still being really challenging. However, if developers really don't like this scenario, then an alternate proposal is to simply reduce the benefits of leveling.
Don't make a level 20 character exponentially more powerful than a level 1 character. Perhaps a level 20 character can easily dispatch several level 1 enemies with ease, but he isn't so powerful that six or seven or them can't overwhelm him and still defeat him. That would make a more believable game since it's not like humans ever become superhumans. Even an elite soldier, caught off-guard, could be killed by a lowly foot soldier with no training.
Now the game can still remain reasonably challenging no matter what level you are. Parts that gave you difficulty at lower levels will definitely become easier at higher levels in that case, but will never become a total breeze where you can just stand there while taking nil damage from low-level enemy attacks once you reach a sufficiently high level. All enemies can be lethal in that case no matter what level you are and no matter how fancy your equipment.