I just got around to finally read all of prillya after watching the anime some time ago and for me it's the ending that was needed to this part,
We know nobody is gonna die, while it's fate, it's still supposed to be a magical girl Illya story, making everyone die isn't gonna happen, at worst a sacrifice, but the way kuro died was way to fast for me to even consider her not being the main objective of illya after all this, miyu also dying was unexpected though, but that goes with fate, putting Illya through the worst despair so she can grow faster, except this time unlike other, she'll probably be alone, when before she always had help.
Also this is a perfect cliffhanger to prepare for next season, everything is put into place, the final boss is here and for the first time, illya is gonna be real pissed off against someone because she just lost her 2 girlfriends, but we also know for some time that illya a grail, so I'm really guessing she's gonna get a power up that goes around this and the zwei form, since it's a big part of her that hasn't been used yet, maybe she could start making her own card or even summon heroic spirits, since the grail is supposed to be a big part of making the war.
While I do see the links to fgo, I really don't think we're going the lostbelts way, It'd be really weird not to go the good ending after spending so much time making your character a believer and wish maker at worst a bittersweet ending with maybe miyu finding a way to save the world just by staying there, but with the destruction that just came, I'm way more enclined toward a fusion of the two worlds, and an endings with everyone together, but we'll see since the road to the true end of Prillya is still a long one since we're just starting the 4th part
But yeah for all that are not envoying this, I mean just stop reading it, there's so many amazing mangas/animes out there, just come back and check later if the new chapters reinterest you, I really have a hard time listening to people that aren't enjoying x anime or manga, since I already don't have time to watch everything that I like, why would I bother with what I don't, I really feel people should just focus on being positive and what they like, especially with all the shit going on in the world now.