I don't understand what it is with people and "horizontal progression." the only real difference between the two is one makes you lug more crap around at any given time to achieve the same results. I suppose it can be argued that it gives more content purpose at any given time but other games make up for that in other ways to still offer the same amount of content in the end for the people who want to collect everything.
Games generally moved to "vertical progression" because the prospect of making bigger numbers do bigger things drives content to help retain players vs the next sidegrade that doesn't really advance your character measurably, which makes it harder to get excited about it. The only issue I have with the way games like WoW and FFXIV do it is they don't vary the formula a lot from one content release to the next. But that's not a fault of the progression style, it's lack of creativity on the content creator's part.
The "horizontal progression" is primarily what deters me from playing many jobs to the same level, because I don't want to deal with mules and inventory management aggravation. It does allow stats on equipment to be more interesting and unique, which is fun, but it can be frustrating in a game that really wants you to play many jobs/classes.