NPC's, in particular the Scions and Grand Company Leaders have made mention of "Warriors of Light" of the past. By adding an S to Warrior it makes it plural meaning they are mentioning more than one. We can conclude that there is not just one Warrior of Light floating around. Even the Warriors of Darkness made mention that they were once the Warriors of Light of their world. That means all five of them. In the interview you quoted he said "Not everyone is warrior of light material." meaning that there are exceptions and that there are more than one but it's not a role than can be applied for and accepted like a job application.
Yes but in canon lore that armor is also a symbol of lies and oppression of the people of Ishgard given who the Knights were and what they represented and protected. They were lead to believe something that wasn't true for thousands of years and offered prayer towards under false pretenses. Why would someone be so willing to hand out something that represented so much wrong in their religion and standards after their true intentions became known?
Not all nations in the Eorzean Alliance are prone to violence against their enemies should they choose to desert their former nation. Gridania I'm sure is one such nation who opposes such tactics unless it was absolutely necessary. Deserters are not initially seen as enemies of a nation they flee to - most of them left their former nation because of the acts they committed either initiated by their own hand, against them or to someone they knew.
