Bhishma was capable of destroying all the Daityas and Danavas in a single day; with how much ease then could he kill the Pandavas with all their soldiers and followers.
एकाह्रा हि रणे भीष्मो नाशयेद् देवदानवान्। किं नु पाण्डुसुतान् युद्धे सबलान् सपदानुगान्॥