I agree. after phase 4 on endless mode, enemies actually become strong enough to kill us in one turn. so, we cannot pass one round without attacking.
but the thing is: when we go further, base values of dice are getting weaker and weaker even if they are fully upgraded. and after certain point these dice are not enough. not just for attacking, blocking also becomes problematic. terrain dice would help about this value problem but sacrificing one round for terrain die might actually end the game. the only solution comes to my mind is being bulky enough (100hp maybe?) to absorb the attack when we use terrain effect.