More Horizontal Progression please

[Reinha]

Soul Sucking Necklace
30 Vitality, Strength, Intelligence

Fatal Lifetap:
10% Chance on any hit to deal 584 unaspected damage and heal's caster for 584.
This is good for all melee, all tanks, all mages. Sure, it might be better for tanks overall. However it can still help mages and melee too!


Life Siphoning Earring of Energy
30 Vitality, Wisdom, Intelligence

Engorged
Slowly converts 500 Life into 300 Mana every 4 seconds.
This is good for all mages and casters. Some other classes may benefit more. However all classes can use it!


Bracelet of Stone
30 Vitality, Wisdom, Strength

Stoneskin
Reduces damage taken by 5%. Slows movement speed by 15%.
This is good for all mages and casters and tanks. Some other classes may benefit more. However all classes can use it!


There is no "BEST ITEM" if made well. All items are different and some have weaknesses attached to them. They just change your "Playstyle!"

This is a no brainer.

Fatal Lifetap for dps because it's the only one that comes with extra damage.

Engorged for healers because the other bonuses don't help them heal the group.

Stoneskin for tanks because a damage reduction is usually way more valuable (smooths out damage spikes, reliable, helps with tank busters, works against magic damage and doesn't interfere with healers) than an RNG-dependent heal (only activates after the damage has been taken and can be wasted as overhealing). Tanks are also the role which has to deal with the least movement/dodging, so that's another reason why it's good for tanks.

The only valid playstyle flexibility comes from the choice between Fatal Lifetap (dps, self heals) and Stoneskin (survivability) for tanks, and this option is already in game in the form of strength and vitality accessories. You say that horizontal options just need to be made well so there is no BiS, but without situational stats like elemental resistances people will always figure out the most optimal gear setup for their role. You can be a BLM with PIE gear right now, but everyone knows it performs sub par. Why on earth would a BLM go for the Engorged bonus when it's painfully obvious Fatal Lifetap is the better option?

Don't get me wrong, I would love some special procs and bonuses on gear. But there will always be a Best in Slot item at any point in time, unless they make boss mechanics which require stacking a certain stat. In which case we are in a lot of trouble with our inventory space. "Different but equal" gear is a nice dream to have but in most cases raw maths will prove one better than the other. That's why I prefer vertical progression with some variety in effects, sort of like "the new tome gear is better than the old no doubt but this time we get to have a damage proc instead of leeching". One way to do this is set bonuses, another would be weapon enchants limited by item level.