Can anybody give me advice on the last cls tier?

The advice I saw and followed, which allowed me to beat it on first try was.

Save Han's taunt for wave three. I used smokescreen on R2 in the first wave on himself. Everyone just killed the troopers in order.

Save Leia's stealth for when R2 has already stealthed her for big damage.

Put your best health mods on Han and R2. If you have good crit chance/damage mods, put them on Luke and Leia otherwise just put your best mods on them.

Your kill order is dictated by the taunts so nothing fancy there.