What's the point with that quite lackluster story in Endwalker?

[Sicno]

Mmmmm not really. The most Dynamis manipulation from an Ancient we see is Hermes, whose noted as being the only one to change the Elpis flowers colors.

You may be confusing this. He was the only one for whom they changed to BLACK (or purple-ish) specifically. That's why Meteion wanted you to change it to black too, so he could see he wasn't alone in his sorrow.