Sayoko is both a healer and a big defense boost for your front line, so I still use her at level 85.
Rather than 1 ruby gacha a day, do the 300 ruby quest by buying 5 stamina and 1 phantom gold, you
get 90 rubies back from the quests, and a lot of union chest points, xp, and materials.
While phantom gold costs start low, they spike up fast around lvl 75... your stockpile will vanish
very quickly.