“Karkat half-arsed it and caused his own mutation”
The process of Ectobiology is one of the very few instances of a self-creating time loop in Homestuck, more importantly the entire process is limited to pressing a fucking button. If you are putting literally any effort into it, you are putting all of the effort that is possible to put into it. It’s not POSSIBLE for Karkat to have “half-arsed it”, it is also not possible for him to have avoided his blood mutation.
The rest of this submission is however canon. Karkat was the one who made all of the Trolls and it seems quite apparent that the ancestors are always created by one of their descendants.