the other thing that's a big negative about eternalism becoming a more and more prominent part of the narrative is that the infinite parallel options steadily suck away any sense of importance from whatever event is happening, meaning that the narrative has to fall back on ever-cheaper infinitely escalating stakes in order to maintain any sense of tension.
so, look at it like this--so, sirius is from a world where jade was a harry potter fan jalker baby was named sirius, and orion is from a world where jalker baby was named orion. cool, i get that. but this means that there's an infinite potential amount of jalker baby reskins. where's the baby from the world where he was named sirion? where's the baby from the world where he was named jalker? where's the baby from the world where he transitioned?
when the writing leans on foregrounding a multiverse (and, even worse, a multiverse without a consistent set of rules) it eats away at the bone marrow of the storytelling. you start to realize that there's no story reason for these characters to be these characters--they've been selected for marketing appeal, picked because they stir up an exciting sense of rivalry and factionalism in the fandom that's well-suited for advertising itself.
'but you're being ridiculous and obsessed with imaginary purity; all stories that make it to the shelf as a product are products and therefore have marketing involved with their writing.' this is absolutely correct! usually, though, and in well-written media, the influence of meta elements on the storytelling are camouflaged. you're not supposed to notice them and be thinking about them, because when you realize "oh it doesn't matter what any character's personality is--whatever the writer wants to happen will happen because they need to sell a product" your investment into a story that you've realized is much more like a popularity contest becomes nil
