The Unsullied is too weak, i'm with war with the Stormlands and with the Westerlands (doing an Aegon rp) and everytime i go in a battle, i always expect 40+ casualties (yes, my army is pure unsullied, no other troops), in a siege, i have more casualties than usual, like 50+, i get annoyed by this because i paid 75k to get these troops, i had better experience with Tyrell House Guards, i get fewer casualties (10 below.)
Is there any way to improve the Unsullied?
Unsullied are terrible solo. So a 70% Unsullied 30% archer mix and NOONE will bear you on open field. As for siege, drop some Unsullied into your castle and grab some levies to act as fodder. I personally run with 120 Unsullied, 100 veteran Lys archer, 9 companions and myself as heavy cavalry and 20 veteran Freeriders. I've never lost more than 8 troops. That's versus armies nearly twice my size too.
That's your problem has H well said. Your army is unbalanced af, Unsullied are excellent spearmen and infantry, but you will not win wars if you have no archers and no cavalry, that's like unrealistic.