I’d like to add my two cents too (and I hope you don’t mind)! So the line mentioned on the Wiki exists and indeed suggests that becoming an Angel is a possible outcome for people who walk the Path. Several lines say the same thing, but others tell a different story. The problem is that the lore is very inconsistent when it comes to Faith and her region.
According to NPCs, the Pilgrimage either awaits everyone Faith captures or is only for those who resist her and fight the cult. Some say it ends at the statue of Joseph, others that it leads to her bunker (and even that walking the Path is the only way to find it). Angels are either made in Faith’s Gate only, at the Convent… or everywhere in the region. When pilgrims reach the statue, some people say the leap of faith is meant to kill them while others (including Faith herself) say they jumped and survived, which we know is possible because the Deputy and the Marshal did it.
Along the Path, we learn that “the Bliss is gifted to disciples who are too full of fear and doubt, elevating them to Angels who can better help prepare for the Collapse”, which suggests Angels already were members of the Project who started doubting, and Faith gave them bliss to keep them under control. However, in a (maybe deleted) letter, a cultist wrote, “Faith is also to lead more new followers along the Path, to reinforce John and Jacob’s numbers. Those that fail can become angels, drafted to serve her other purposes”. This would mean that walking the Path is simply a way to join the cult and you only become an Angel if you fail. Oh, and there’s The Misery, too, and it’s apparently for people who refuse the Pilgrimage…
Faith reportedly controls the Angels and is the only person who is immune to the effects of the bliss. Pretty much all sources confirm that a high dose of bliss is what turns people into Angels. That can happen accidentally because of repeated exposure, for example if they stay in the Bliss for too long, or be done to them on purpose. In real life, I don’t know of a drug capable of effectively and permanently brainwashing people and “zombifying” them, either, but bliss is basically magical so I guess it can totally do that!
Some people explain Faith “keeps the Angels dosed on bliss” by lacing their food (dog food, according to rumors) with the drug. I’m not sure why that would be necessary, though, because everyone says Angels can’t be saved and that the effect of bliss on the brain is permanent (it “passes the blood-brain barrier” and can never be “purged out”). According to a note, Angels are saturated with liquid bliss because it has a “better resurrection rate” compared to powdered bliss (despite the fact that the latter is “more powerful”), and that’s why they can get back on their feet after being shot.
Anyway, as you can see, things are a bit unclear, to say the least. I’ve personally decided that Faith makes everyone she gets her hands on walk the Pilgrimage and take the leap of faith so they can get “enlightened” and then potentially join Eden’s Gate. Those who aren’t “worthy” either die along the Path or don’t survive the jump, and those who resist or cause too much trouble get turned into Angels so they can still be “saved” and part of the Project, and the same fate awaits followers she thinks aren’t faithful enough or have become a liability.
Now, I’m not sure Faith’s message suggests that Angels’ mouths are surgically altered… Here is what she says:
Have you seen their faces? On the Pilgrimage? Oh, you should see it. To see the sin fly from their heads and their faces slacken to peace. The vanity shaved from their heads, evil taken from their lips. Never to speak a sinful word, any word, again. It gives me life. Every time a bell rings…
To me, this simply means that the drug alone prevents them from “sinning” because they can barely think for themselves and don’t talk much anymore. Also, we know Angels “sing” all the cult’s songs, so they’re definitely able to speak clearly. I’d say the mask is either meant to keep them exposed to bliss at all times, as you suggested (even though they’re already permanently brainwashed), or I thought it might be some kind of muzzle. Maybe it’s both.
As for the Angel apparently being “made” in John’s Gate, I’ve always thought it was weird because, when we’re in his bunker, he says:
Things could be worse, you know… here you just have to confess. In the east… well, let’s just say too much Bliss can go to one’s head. Faith created her “Angels” but never did treat them all that well…
And this, to me, suggests two things. The first is that people only get turned into Angels in the Henbane River, not the Holland Valley. The second is that John doesn’t seem to be a fan of them and the way they are treated… so why would Angels be created in his bunker? I understand it’s scary and challenging to have them in this mission, gameplay-wise, but I really don’t think it’s logical, story-wise.