They're a source of ISO and 7* Shards - nothing more.
Just to try it new champs from featured crystals
Depends on where your prestige is and how long you've been Valiant. I'm like 4 months into Valiant status. My sig200 Doom and Photon are both still lurking in my Top 30 ahead of various R2 unawakened champs.
I care about them just to use them for Featured 6* crystals and to try to get new heroes. Right now waiting for 6* Dracula and Frankie.
I cant even remember the last time that I ranked up a 6* except for fun! I definitely dont have any use for the resources and sell them for gold