Like a lot of challenges in this game, it's really hard till it suddenly becomes really easy. I used to have a lot of trouble with Tier II but I was pleasantly surprised this time with how my team fared. CLS and Raid Han undoubtedly were the MVPs, but everyone played a role. Just as a data point, I ended up with the whole team at around 80% protection or higher. My team FWIW -- mostly 7-star, lvl 85, g11, full abilities except zetas (with exceptions noted):
CLS lead, speed and potency set mods, speed arrow, crit dmg triangle, 224 speed
R2-D2, (Number Crunch zeta), speed set mods, speed arrow, potency cross, 260 speed
Princess Leia, crit dmg and health mods, crit dmg triangle, 251 speed
Han Solo, (6-star), crit dmg and crit chance mods, speed arrow, crit dmg triangle, 202 speed
Sabine Wren, crit chance and health mods, speed arrow, crit dmg triangle, 196 speed
Best counters to the last round are speed, TM steal, taunt, and stunning the royal guards before they stun you. So Ackbar lead is good, and ST Han is likely useful, or Old Ben. Plus obvs R2 and Han Solo. Tenacity is probably also useful so Farmboy Luke lead is a good second choice. Wedge is also a great leader choice in almost any situation.
Good luck!