How many Warrior of Light exist in story?

[Eloah]

I do not believe possessing the Echo makes one a Warrior of Light, because it seems to be an unspoken thing that the Warrior of Light's Adventuring allies also possess the Echo and thus are immune to tempering.
The primary qualifier to be a Warrior of Light is possessing not just the Echo, but ALSO the Blessing of Light. The two appear to be two completely different powers, as when Midgardsormr took away the Blessing of Light in 2.55, the Echo was a power our characters still retained. If anything, to have the Blessing of Light would require one or more Crystals of Light as well. The only other person with the Echo who also had a Crystal of Light that we know of is Ysayle, but that wasn't any indication that she had the Blessing of Light.

GAH!!!! What I originally wrote got deleted, I hope this is similar to my original, T.T

You are misinterpreting the context with the meaning. Similar to what Moose said, the phrase Warrior of Light has different connotations based on who and when you ask. In the present time the current usage is because the people are referencing the "Warriors" of Carteneau, whom they can only remember with a flash "of Light". But anyone with the Echo is one of Hydaelyn's Warriors of Light, they are just not referred to as such since that phase means something different to them. This is confirmed canonically by the 4 individuals I mentioned, The Warriors of Darkness, Y'shtola, and Matoya. But as I mentioned before not everyone with the echo will rise to prominence like the 4 we know of, some might not even know what it is as it manifest differently in each individual. But as someone mentioned in a later post, we do seem to be Hydaelyn's "pet project". Basically its like this, if you have someone doing something for you and they are doing a good job, you're gonna make sure they have the resources and tools to continue doing that job. Basically we are helping Hydaelyn, so she is helping us help her i.e. she gave us the blessing of light.

The Player is the official 'Warrior of Light'. To be fair that is a label given by the public so really the fact only the Player is recognized as the Warrior of Light is because no one else has been yet. There can be more than one Warrior of Light at a time. Storywise, the Player seems to be specifically Hydaelyn's chosen champion. Both Midgardsormr and the Ascians seem to suggest as much. She has many agents but the Player is a special case and Hydaelyn invested a lot of energy to protecting the Player while they grew in strength.

I'd say that's about right