21 Gilded Crests per week. That is slow but better than nothing. It’s useless if you can hit M+7 and up. (+7 drops Hero gear. +8 drops gilded crests).
But if you cant access M+7, Delves is everything to gear up all the way to 626. 619 and Hero gear from Vault. You need Hero gear to upgrade it to 626 with Gilded Crest which is equal to 45 Rune Crests right now.