Would Horizontal Progression Help this Game?

[SchalaZeal]

Short answer, yes.
It has to be quite demotivating for devs to spend hours on creating a content knowing it will be obsolete in 3 months.

Actually lots of people play content 1 patch after its out. Even 2 or 3 patches after. But rarely 1 expansion after (and that's 2 years) if you had a level increase.