In vertical, things are better for sake of beign better. Bigger number, bigger something and bigger e-peen.
In Horizontal progression things are better because they behave better, have characteristic that other things don't have or do some things much better than other things (in other word they are much more specialized and focused on single thing).

The above is something that Inside said and I think it deserves not to be drowned out Duelle clearly does not understand the difference here as he believes that it's the same.

I'll break it down. In vertical progression the new gear is better because instead of having 10 strength it has 14 the only reason you wanted the old gear is for the 10 strength and then the only reason you'll want the new gear is for the 14 strength. The only reason the mob is stronger is because SE (some celestial being of eorzea) came in and magically made new things in the world twice as strong as everything else.

In horizontal progression the gear is better because it has 10 more evasion and our tank is absent (time to show my pgl stuff) still other gear is better as it has strength, yet another piece is valuable because it enables me to use abilities faster.

You don't need macro swaps for this I already do it in XIV (that's right i have 3 pieces of gear about per slot per class) so no this is not about macro swapping gear at all. You don't get this kind of development with vertical progression because your options are diminished you don't get to choose between 6 varying pieces of gear your choices are narrow to one or two pieces and they are not very flexible pieces either.