I don't really get this logic. What you're essentially saying is the game would be better if it just ended after X hours before you had a chance to see too much of it.
No, my logic is that spending devleopment time and resources to add lots and lots and lots of areas forces developers to recycle ideas and half-ass some designs, so some of the dungeons in the game won't be as good as the others. The quantity of the content leads to some of this content being mediocre compared to the rest.
The game would be better off with half as many dungeons, but they get twice as much effort invested in their creation so they're all unique instead of copypasta'd clones of each other.
When a similar idea gets recycled often enough, it stops being interesting. In Skyrim, fighting a dragon was cool for the first couple times... then it became routine and finally an annoyance. Had they stuck to fewer dragon fights, they'd be more memorable and fondly remembered. The way it is, they became routine and were turned into a meme due to their frequency. Same with the dragon claw puzzle where you have to look at the claw in your inventory to see the pattern that opens the gate. It would be a cool thing to have it once or twice in the game, but when you get the exact same simplistic puzzle a dozen times, it becomes routine and boring. Same with the inactive protectrons in Fallout 4. Same with the activities in Ubisoft's open world games, where the exact same activity is placed a dozen times across the map.
Copypasted content is lame and boring, but if you make each quest and location unique you won't be able to make 200 of them. I'd rather have a game with 30 hours of content but all the content is unique, than a game with 300 hours of content but everything you see after 10 hours is just a copypasta of what you've already seen.