I have simple answer. The simplest solution and the best one for balance is to set some checkpoints like: coming to fort joy, finding way in magister's headquarters, getting out of it. etc.
Side quests and killing should only give items and money as reward, because they don't directly help in progress main quest. They will be pure optional choices.
If you want level up you need to actually progress, no backtracking or randomly kill everyone.
That solution doesn't force anything, and is nice gift for people who only want to do main quest only. People who like doing combat, quests and stealing will have extra items, skills and gold.
I'd be fine with this tbh, as it doesn't remove the reward for doing extra work / doesn't cheapen then decision to spare/kill bad guys.. but would uncouple the level/power imbalance and keep the game challenging even for the evil hobo barbarians everyone keeps mentioning (I imagine they are also cannibals amirite?)
Also, I ,patently, hate this idea. Removes weight of actions beyond simple gear and money.....which one can make or buy easily.
Why would anyone kill anyone if it doesn't get you anything unique? When it ultimately matters nothing? When it hardly changes the experience directly?
No, uncoupling XP from combat and direct actions is never something I could agree with.
XP for killing XP for significant trigger actions XP for discovering new locations
I still find this very silly argument when it amounts to little beyond saying: "That guy worked longer, but doesn't deserve more; even when the end difference isn't that big!"
