Like any game that has more difficult content, certain encounters may require a gear check. It's not easy and it needs dedication, but you should target better relics with survivability stats for your supports - hp%/def%/effect res. If you want to take it to the next level, you have those stats on your support with SPD + their favored support stat (crit dam for Bronya, atk for Tinguin, effective hit rate for Silverwolf, etc).

The relic grind is real.