Well given how many people play FAF it's not surprising that you'll be able to find someone that thinks T3 arti is overpowered at any point in time.
That thread was also on the balance forums which have specific guidance that is meant to be followed.
Anyway if you want an easy solution to defending your core base from 1 T3 arti, get a couple of T3 shields spaced out to cover your base, and assist each one with a bunch of T3 engineers (I've forgotten the best number, but around 12 is probably ok). It'll use up resources but you can cost efficiently defend against 1 T3 arti, and if you were performing evenly to your opponent until now you should have a lot of mass saved that was invested into experimentals/units that can now go and kill them while you hold off their T3 arti.