Rework ilvl?

[Felis]

But it's also not difficult to see why a vertical progression model attracts players better than a horizontal progression model (which appeals to a much more niche population). I don't think it's much of a leap to say that most players of RPGs want to see their character get markedly stronger over time, and to find that the things that used to be challenging, as they increase in strength, become easier and easier until they're eventually trivial.

Exactly.
And it is not something new in RPGs. Since the first RPGs on Nintendo you find stronger equip in the next town than in the previous town. Always you reached the next town in the story it was time to buy new equip.