Why a KE shield breaker:
In a duel it's not hard for someone else to bait and survive 10 sawa shots, especially if you're not really experienced. If all you have after that are sniper rifles, then the enemy can pop out a KE shield and win handidly.
There's also the fact that this AC has such low AP that it needs to be aggressive and drop the enemy's AP early on to get a lead. If the enemy is running 2 shields and high AP, it's easy to waste all of your sawa shots trying to take the shields down, leaving you with just a sniper, again.
Why a KE shield:
The KE shield shuts down counter sniping and rifle/HSM stunlock, two common weapon sets that can stop something like this easily. X00 and SRB aren't accurate enough to trade sniper shots with subcomp'd SRA-133s or Kumoriyo Mdl.1 at 250-300+m, espcially with only 120 firing stability. And once X00 is purged, you're in the range to be stunlocked by a lot of weapons.
A CQ version of this build may not need the shield play, but I'm of the opinion that if your build avoids being shut down because other people aren't paying attention to you, eventually people are going to start specifically targeting you and lock you out at the end of a team match and force you to change or find another team to fight. Duels are much more my experience than CQ, so take that with a grain of salt.
Also, Sash and I are talking about 2 slightly different builds. He's talking about a dual arm rusher (I think) with VTFs or EN amps, which is in and of itself a very good build, but a lot heavier and drainier than what I was suggesting. Probably using BA-309
I'm talking about a single-arm (or no shoulder) rusher that is quite a bit faster, that only pops out of scan mode to fire the guns. Probably Niodori Mdl.1/Niodori Mdl.1/Shotgun/Howitzer on 177 no-shoulder arms, Tokonatsu, and the highest output gen that gives you rushing cap. Basically, trade VTF spam for being able to stay out of melee range and about ~50 more glide boost speed.