Are FFXIV tanks just players who "couldn't hack it as a DPS"?

[Atreides]

When it comes to the difficulty of being a tank in FFXIV, I think it stands for itself that most tanks are not concerned about how to become a better tank, but rather how to become a better DPS.

Same with healers though, this game is all about DPS. Moreso than any other.

The ideal situation is if they don't need to heal at all and can reduce the healing to only off global cds.

You can't blame either though because this is how this game is pretty much designed, even though it's not as tight with the DPS check as it was in Gordias for example it is still pretty tight in harder content so the mentality to DPS sticks to you at some point.
Unless they force tanks in tank stance and reduce healers damage output outside of solo content drasticly this won't change.