If you're talking about progression with narrative, Divine divinity/Divinity dragon knight saga has it. If you are hovering your mouse on the stats, the tooltip will say how powerful you are compared with other heroes. I noticed that DOS is absent on that kind of feature, but it's not important.
I think difficulty should be fixed right at the beginning of the game to maintain the balance if there is any difficulty slider at all. Similar to Europa Universalis IV system in getting achievements on steam wherein you need to be in "ironman" mode to get achievements or similar to witcher. Ironman mode is having only one save and the game saves in every decisions you do or in a monthly basis. It also disables cheats and whatnot. This kind of imposing achievement gathering is addicting IMO. If you look at the global stats, only less than 20% of the player base actually tried in getting achievement before quitting, less than 1% of the player base actually gets the hard achievement, and only less than 5 actually got the almost impossible achievements.
Although, I could tell that this is not an important aspect of the game yet. Priority very low.
TL;DR impose difficulty at the beginning of the game per the player choice. Player can't adjust difficulty during the game. For achievement hunters, achievements could only be gotten at a certain level of difficulty for added replayability.
