Yes, Susano'o arrows are almost impossible to react to, however if you remember Kirin was supposed to be undodgeable/blockable as well and Itachi had such good reaction time that he was able to use Susano'o before it struck. Kirin is faster than Susano'o arrow as it happens in 1/1000 of a second, and Minato has insane reaction time, so I see him dodging the Susano'o arrows with his reaction time and FTG, since you also can see the Susano'o pushing back the arrow giving you previous notice and gives one enough time to put his guard up. FTG has never been stated to deplete chakra levels quickly as all it is is a simple S/T teleportation using a seal on the kunai. Even if it took a decent amount of chakra from most shinobi, Minato is said to have very large chakra levels due to the fact that he can summon Gamabunta on top of the Kyuubi without being fatigued and using a s/t barrier to redirect a TBB from Kurama to a FTG. you might be right, but for now it is only speculation, so one can not put trust in such a thing, as it is merely an assumption.