New to Warhammer, HOW DO I PLAY SKAVEN WITHOUT THEM ALL COWERING?

Recently went up against the big tree guy dorphu. Auto battle said “decisive victory”, but that’s boring and I wanna see my rats blast them away with their mini guns. However, my rats would break before taking a lot of damage. I lost miserably, my rats gone, my heart broken.

Do I just suck? Or am I missing something?