Originally Posted by
Nektulos-Tuor
If your needing to constantly switch out gear. Then that isn't horizontal. That ... is pretty much just vertical with needing different sets of gear.
Horizontal Progression means you can do content with any of the gear available, you just pick which one suits your play-style, trade-offs.
If you have to carry a set of gear for each content you do then its already just vertical progression with more sets of gear needed to do the job, for example gear that is better against skeletons. Now to take on the skeleton raid you need skeleton armor. That isn't horizontal. That is still vertical.