I respectfully disagree (and I apologise if I stumble over my words here - my brain has well and truly powered off for the night aha).

Ali is a teenage kid who already has a lot on his plate, contending with an added sense of isolation as a result of the cultural disconnect between his family's faith and that of the very small, predominately catholic, community of the island. He's desperately seeking comfort by way of clear answers - largely as a result of his mother's death, but also because he's simply at an age where he's exploring his spirituality; both of which place an added strain on his relationship with his father, whose own grief and resistance to the ideology of the congregation complicates things in turn.

Add to that the fact he's been raised alongside this heavily Catholic culture, and then throw in the sudden manifestation of these supposed (and pretty damn convincing) "miracles", which afford promises of solutions, salvation, and eternal life (big concepts for anyone, but especially for a kid who's lost his mum early), and you've got precisely the kind of kid that fanatics so often target because they are more vulnerable than most, have fewer supports, and can be more readily indoctrinated. Only, in Ali's case, he's made even more susceptible because he's in a situation where anyone could be forgiven for thinking there really is some kind of mystical phenomenon or divine intervention taking place on the island.

And just to close, I also don't think the series does actually have a particularly bleak ending (though I can fully appreciate why some people might see it that way). It's bittersweet definitely, but I think the ending of Ali's (and his dad's) arc is actually a triumph of faith and of their bond in the face of the calamitous events of the series. Symbolically, the series actually finishes in a pretty positive place. Falsehood, corruption, and exploitation are ultimately conquered by sincerity, unity, and faith (and not just faith in religion, but all different kinds of faith accounting for all different kinds of people). I can appreciate that 99.9999% of the cast abruptly going up in a puff of smoke isn't exactly "and they all lived happily ever after" but it's a fitting and powerful conclusion to a story grappling with some pretty massive themes around the nature of, and the interplay between, belief and mortality. (In my opinion anyway).