It’s quite a bit of work, yes, but fortunately they already have a lot of data to do it. Fixing a mob’s level is no more difficult than taking it’s scaled value and settings its level range minimum and maximum to the same number.
If you want to do an exceptional job you will of course add some new spells and funny tricks to the harder ones.
As for quest ranges, be a little lenient. Take the hardest mob in the area of the quest and subtract 8 - or maybe just leave them all at level 10. If you are concerned about twinking - which frankly can be solved by just removing the XP lock - simply put in minimum level to equip instead of to take the quest.
Make the number differences smaller between the levels and disable defence/hit rating in PvP, but keep it in PvE in such a way that being max level gets you hit capped against anything. At low levels, however, you will suddenly face a steep punishment when fighting higher level mobs despite the health and damage differences appearing rather small.
Raids take no damage, you get progression, and PvP takes no damage. You no longer need ability scaling against low levels, either.
And now we’ve solved some problems. A LOT of problems, actually.
Don’t understand what you want to play RPG’s for.
In Skyrim Requiem, which I mentioned earlier, there are 3 types of wolves. The basic one is level 2, the dire one is level 5, and the frost one is level 8 and has frost resistance. Once you’re levelling 11 you can destroy whole packs of them, though more often than not they’ll try to flee from you if you approach, which also clears the road for you so you don’t have to bother with them.
Meanwhile a Vampire is level 25, some are level 40, and Harkon is level 125! If you try to take these on at level 11 you’re going to be in serious pain, but as you level up you’ll find vampires get easier. Eventually however perhaps it’s time to look into some Daedric artefacts.
Mehrune’s Razor is very, very powerful but you best be level 50+ to deal with the rapidly attacking invisible entities that can only be seen with Detect Magic and move incredibly fast, but are weak to lightning spells and therefore particularly weak to lightning runes as this will dispel their magic and make them visible.
This in my opinion is how you make RPG’s. This is what D&D does at well. It’s so much fun - you really feel the growth, low level trifles end up not hurting you and things that are stronger than you encourage you to push on into dangerous areas, but you’re constantly evaluating how strong you are and feeling it change upward every single hour of play.
Of course this also means that different areas of the world have different inherent difficulties. Bad idea to just sprint straight to Solstheim because the Ash Ghouls that spawn there will throw an Ash Bolt at you and blind you, then 1-shot you. But if you’re a level 30~ish player with some fire magic or an enchant sword and a shield you can block the Ash Bolt (or dodge it I guess) and then burn that thing alive.
Oh, and dragons? Be careful - you ain’t killing one in level 5, that’s for sure.