How many Warrior of Light exist in story?

[Alleo]

Interestingly we can even see our allies in steps of faith . After the fight we see them in a cutscene, its the people we collected earlier by asking around. I found this to be quite a interesting cutscene and its also the only one that truly shows that we had other people with us there. I am still of the believe that we slay primals alone and that also most of the story dungeons are done alone too otherwise it really does not make sense quite a lot of time. But that can probably be discussed endlessly so I am stopping my little off topic here.

[Cilia]

Interestingly we can even see our allies in steps of faith . After the fight we see them in a cutscene, its the people we collected earlier by asking around. I found this to be quite a interesting cutscene and its also the only one that truly shows that we had other people with us there. I am still of the believe that we slay primals alone and that also most of the story dungeons are done alone too otherwise it really does not make sense quite a lot of time. But that can probably be discussed endlessly so I am stopping my little off topic here.

Those characters were winners of a contest in which players who won would have their character appear in-game. The same is true of the Miqo'te woman Thancred is chatting up on the balcony during "The Parting Glass."

[Enkidoh]

Interestingly we can even see our allies in steps of faith . After the fight we see them in a cutscene, its the people we collected earlier by asking around. I found this to be quite a interesting cutscene and its also the only one that truly shows that we had other people with us there. I am still of the believe that we slay primals alone and that also most of the story dungeons are done alone too otherwise it really does not make sense quite a lot of time. But that can probably be discussed endlessly so I am stopping my little off topic here

That's not completely correct in that instance is not the only case of your party appearing in a duty cutscene, in the Praetorium your party appears with you in the cutscenes as well, such as when you first jump off the Enterprise, and the scenes with Gaius and Nero, all the way to the bottom against the Ultima Weapon, your party members are standing around behind you (and some even have little gestures they make to each other!). But given the tendency for players to skip these cutscenes, it's little wonder that is missed (and hence wouldn't occur usually when viewing those same cutscenes later in the Unending Journey).

Either way the storyline specifically mentioned just prior to that quest that you were told to "lead an elite adventurer unit into the Praetorium to destroy the Ultima Weapon" (paraphrased), which makes sense, given it was a military operation taking place under the auspices of the Alliance, you weren't just trudging through some random ancient ruin there.

As far as Primals go though, some Primal fights specifically mention that your player is the only one there (such as Ifrit NM, because your character was naturally captured by the amalj'aa due to Ungust's plotting and was dragged there to be tempered, and Ravana HM, where again the player is sent to be tempered, although this time they're accompanied by Ysayle and willingly let themselves be captured).

Other Primal fights though it's less clear though, with some seeming to favour a "find a group of your most trusted companions and then take down the Primal" approach, Leviathan especially.