Hmm ...

What's the main job of a tank ? Making the raid take the minimal amount of damage.
What's the main job of a healer ? Keeping everybody alive.
What's the main job of a DPS ? Making the raid do the maximum damage and not taking avoidable damage.

What's the sub job of a tank ? Help the DPS by doing some damage and the healers (Ot castinf Stonskin is an example).
What's the sub job of healer ? Help the DPS in some fights (plumes vs Garuda EX is an example).
What's the sub job of a DPS ? Nothing (except for BRD).

In end-game content, if the DPS is too weak, the raid wipes. So, gimping your DPS for more "utility" is a no-no.