What's the reasoning for melee jobs to have three different sets of gear?

[wereotter]

Now realistically, I'd argue it would make more sense to make Ninja instead wear Aiming armor instead of trying to combine them with other melee.

Please no to this, no to ever having this.

As it currently stands, the most intense competition for armor in the game comes from trying to get loot from the 24-man raids.

Tanks can always roll need on the gear for their job if they want it and get it since even though there are four tanking jobs, there will only ever be one in the party.

Healers always have to compete with one other healer.

With 5 DPS in a party, if four jobs shared gear, the possibility of having to roll against 4 other players who can all wear the same item you can is a very real possibility, especially if those four jobs are among the most popular in the game.

Also I will say that keeping multiple sets like this is likely an intentional method to keep people playing the game. More distinct armor sets means more grind for gear if you want to have good gear on multiple jobs.