which is worse, two step-siblings dating or two biological siblings who only met as adults?

let's assume the stepsiblings have been stepsiblings since before they were teens and only started dating as adults, and the biologically related siblings didn't know they were related when they started going out, but just disregarded the fact after it was discovered and stayed together. which pair is more morally wrong? i ask this because even though i believe all forms of incest are revolting, many people often cite either having deformed babies or a power dynamic as the main reason for acts of incest being immoral. but what about when the couples are the same sex/don't want kids anyways, or a power dynamic isn't all that present? i'm not saying that most incest isn't the result of grooming or heavy power dynamics, but i'm also not claiming that those aspects are present in all incest relationships 100% of the time. i'm just trying to grasp how the majority of people feel about this.
P.S. this isn't a debate about whether incest is okay or not