FFXIV usually design healer/tank jobs with different type of mitigations:

1- shield: which is extra HP pool.
2- reduce damage received.
3- increase defense.
4- healing or regen.

I see that there is no different between reduce damage or increase defense.

The differences are clear with Shields and healing/regen.

But when to choose between shield or increase defense?
Or why we have increase defense or reduce damage received?

I wish that we can have a clear way to decide which to choose and when as we currently we have one type of attacks and 1 type of tank busters