For more optimized run see stage 12 where I needed more dps:
• Faction Trial - Piercers Stage 12: Only 1 ...
Only 1 defender means put best dps sets on the 3 dps defending the top portal. Except for Silas, he doesn't need your best gear because his ult makes him ignore a chunk of enemy defence, and he has enough time to get his ult back every wave if you skill him up a bit.
Can be done without Hex. As long as your tank + healer can hold the bottom. Use Luneria 6* magic damage instead?
Sets:
Lili, Nissandei, Luneria: Invigoration (they buff the 3 dps defending the top portal: Theowin, Nyx, Calypso)
Calypso, Hex: Soulbound Arcana + Whirlwind (with soulbound, ult early and often to build up their dmg stacks which means place them as early as you can afford so they start ulting)
Nyx, Theowin, Silas: Infernal Roar + Calamity (or Warlord). Put Theo in front, his ult is the most useful; slows down enemies, more time means means more damage.
Brienne: Fracture + Whirlwind (Actually only had 1 jewlery piece mistakenly), don't need much dps at the bottom. I only use Fracture because that's my next highest dps set.
Livian: Guardian + Immortal Warrior (the best thing for "tankiness" is guardian set all HP% main stat, the more HP means the more they get healed)