By 10% of his health, do you mean actual health (phase 5) or titan's heart health?

If it is titan's heart health, then yes, your group needs more dps.

If its actual titan health, then your group needs to work on dodging and your healers need to coordinate better, not lack of dps.

Fwiw titan post heart is doable with just 1 healer , 1 tank, and 1 dps, though it will take forever.