I no its a hard question and its based on what game and what you do but If I played games on easiest setting how long will they take to complete on average. I always think playing on easiest that the game want last 2 minutes but playing on harder difficulty I always rage quit. When games say 40+ hours is that on default difficulty not lowest. I like the idea of RPG but I always find them too difficult. Take Skyrim I played that many times with many times rage quitting or restarting even on adept difficulty. I am going to play Dragon inquisition which I got cheap and if I play that on lowest difficulty how long will the average gameplay be doing all side quest etc. (Average play time)
Ive not played this be for and even if I do find it too easy I'm not going to change difficulty from lowest as to see how many hours I play and people say that this game is about story any way. Will do the same with skyrim next. Going to start DI this evening.