As per the provided link, there's a number of factors going on.
First of all, a kiai is as much about a forceful exhalation and a focus of purpose as it is actually yelling. Many of the fighters do just that grunting or exhaling on a heavy strike.
One of the other purposes of a kiai is to startle the opponent. In the Octagon, most fighters are prepared for ...
Wrestling and judo were not unknown, but particularly outside of Olympic season generally weren't featured much. Pancrase, shootwrestling etc. were largely a curiosity among pro wrestling enthusiasts.
BJJ was featured in movies like Lethal Weapon but exploded after UFC1.
Let's analyze situation:
"constantly guarding his face" + "block mid punches" - it seems, that your opponent has good reaction and definitely would block single punches/middles.
"can easily evade low-kicks" - that is a sign of good "leg performance" - your opponent is light on his legs, not grounded.
So, what we can ...