the one without armour & survival doesn't only need higher agi, it needs one of the highest agi around, otherwise it doesn't help you against most brutes, cause as soon as your opponent has less agi than the armour & survival brute, the a&s brute is better.
you only have advantages with brute 2 (the higher agi one without a&s) against brute x in the range agi a&s brute < agi brute x < agi brute 2
(this is valid especially for untouchable brutes)