Wait... there is a translation error in both versions of Arges' speech. In the Portuguese version it says that she used Chronos' power, in the English version it says that she didn't even have Chronos' power. I'll download the raw one here and have a look (I'm already downloading Aiolia's raw from chapter 4 of episode g btw)
Even without the Keraunos thing, Pontos in chapter 47 claims that FTL is the speed of the Gods, and recently Shura had to activate the ninth sense to overcome the speed of light.
It is easy to make a list of all the moments that the Gold Saint talk about light speed, or near light speed from episode G to the end of G.A, and most of them when they go to FTL it is because of the Ninth Sense.
In the episode G.A Shura exceeding the speed of the initial inflation of the Big Bang is explained perhaps by the fact that he took some of the power from Chronos, the God of Time. Also, this was not just a "IF", the Cyclops Arges points out how Athena used the power of Chronos while he was watching Shura arriving on the battlefield.