The curious thing is: both of you are right.
I mean:even if the avatar is affected by the decisions you make, he still has his own dialogue.
So it is not truly first person, but not truly third person either.
For example: In Resident evil 3 Jill Valentine is an avatar that the player, uses to move, and make decisions(mostly on nemesis) but she has her own dialogue, feelings, and she is "autonomus". So you dont have the feeling that you are the character, but you are playing with a character. " You want S.T.A.R.S? I'll give you S.T.A.R.S"
This phrase is truly fulminant and it's an indicative that she is a character that you play with and not a "fist-person character".
And another example is: TES:Skyrim, in this game you are truly on "first person", you decide what to say, what to do, basically everything, so it's truly a "first person game", where you, the player is the MC.
In a Struggle with Sin is more like Resident Evil 3 than Skyrim, but because it doesnt have enough bucket to make the player have that feeling, make people dubious.
So stop digging about that.