I see a lot of complaints against vertical progression and that it should be horizontal progression. As far as I can tell, vertical progression means that the stat numbers on the enemy are increased. So you either have to gain levels or gear or what-have-you to increase your numbers to be able to defeat them.
People dislike this. Fine. Let's take it away completely. So now no numbers ever increase. What then is left? The difficulty comes solely now from the AI. New content just has monsters with different AI, but the overall power level of everything stays the same. The end. Does this really change anything that much?
I don't think so. And I think that people who obsess over the so called "horizontal" progression have this illogical fantasy that their character will be non-stop transforming their skills into different skills in a never-ending skill customization system. At some point, your character's playstyle is defined. Horizontal progression has its limits. So when you say you only want horizontal progression and no vertical progression, all you're doing is taking something away from the game, and you're not really adding anything in return.