Horizontal gear progression isn't some perfect system. It brings along its own set of problems, that in my opinion, are much worse than the problems with vertical gear progression.

Lets not forget how in FFXI:
- Real item upgrades were very rarely added to the game. It wasn't uncommon that new patches added nothing for your job.
- To keep players from getting their gear and being done with the game, FFXI had a mix of bad drop rates and lockouts that ensured that you rarely were able to get gear.
- Since we didn't get any real upgrades and items were so rare, we had to rerun the same stuff for years.