The issue is due to two primary factors.

First the biology of humanoids in D&D precludes something like this, doubly so when elven gestation cycles is considered. The differences between drow and other elves is not huge. They have some minor physiological differences, and some minor magical bonuses. They would have to be completely different creatures for this aspect of pregnancy to work. They could have said something like their genetics are so competitive one ends up absorbing the others early in development, like vanishing twin syndrome, because the dominant one consumes all available nutrients killing the other embryos. However the explanation makes it clear they are physically killing each other. This, topped with the erotic element, is just bad world/lore building. Bad lore that only exists to be edgy, which is bad storytelling.

The second big issue is that this is mainline D&D. Mainline D&D is not a grimdark setting. This isn't Warhammer. D&D also has settings for this type of thing. To a lesser extent, places like Ravenloft, which can get pretty edgy, but this would be pushing it, even there. Others would be settings like Dark Sun, which is pretty much built for edgelord storytelling. Though the bad world building surrounding the discrepancies between drow and the rest of the elves would make for bad storytelling even in such a place. If you create a set of rules of nature, those rules can be whatever, but you need to not break those rules. Going through the basic lore of an otherwise typical high fantasy setting, people aren't expecting to come across cartoonish edgelord shit like this.