Why are there so many useless cross skills?

[ShikiRin]

Some examples:

For example Mantra for Dragoon
Increases HP recovery via curing magic by 20% for self and nearby party members

Or Hawk's Eye for Summoner
Increases DEX by 15%

Rly SE, dafuq? Summoner seems to be the most useless class anyways, why give him only 3 useful cross skills?

[Jarinolde]

Hawk's Eye is a bit of a headscratcher, but having Mantra on your DRG gives you awesome party utility. Crazy AoE about to happen? Help your healers and pop Mantra.

[seikenflash]

I find mantra to be quite useful for those hard hitting AoEs like self-destruct. They are not useless you just need to learn how and when to use them.

[Tolmos]

Or cure for Arcanist, who has Physick...