A good workaround to this issue, would be to have limited level scaling. What I mean, is that the enemies should start at a certain level by default, but will also scale up to a certain level (within a 2-4 level range), so as to still provide a challenge to those who do every single side quest and gain levels faster. In that way, casuals will be able to finish at a lower level, but those at higher levels will still be challenged.
I've always been a fan of limited level scaling myself as well, but am surprised at how rare it is. Developers seem to always go for all or nothing. The ideal would be to make it an option for those who want it. I could see scaling being annoying and make you feel not powerful when wolves from the first map could still kill your level twenty character, but scaling of a 2-4 levels would definitely help smooth out progress for both casuals and hardcore players. I hate being overleveled and trivializing content, like when I finally went to the Black Cove a couple levels higher than the enemies there and the combat was boring because the level differential gave me such a huge advantage.
Pillars of Eternity would benefit from this too; that game had even worse issues with over-leveling than D:OS. Basically ruined the game for a lot of people because the second half of the game became so easy if you did even a handful of sidequests. (They've fixed it somewhat, but not retroactively).
