How about adding random encounters that occur more frequently and get more difficult the higher level you are, and at the same time give LESS XP?
If you want to rush through and are able to beat a higher level encounter due to your skill as a player, then great, go for it.
If you are at the "appropriate level" for a certain encounter but can't seem to beat it because you're not as skilled, then you can either go around the encounter, do side quests and gain some gear / level before moving forward, etc.
If you are the completionist that wants to see every single thing before moving on, you can try, but you will have more and more ambushes during camp or while travelling that don't net anything useful and only a little XP. This might dissuade people from doing this and ruining the remainder of their game because they're too high of a level for meaningful encounters and at the same time encourage them to play through a different path on a 2nd or 3rd run through.
Ideally you'll work your way through the story while roleplaying your characters, and the story will be relatively balanced with what your level is at that point.
I just hope we end up with an actual roleplaying game when BG3 is done and not some "hodge podge statistical make the least amount of people unhappy as possible" pile of garbage. Larian needs to build their piece of roleplaying game art and let people enjoy it for what it is. Nitpicking every little thing that is subjectively good or bad can just ruin something like this.
