Seems to me that parents should want to minimize that suffering, even if I also disagree with “owing them everything” as parents should also help them to grow into self-sufficient beings. It’s a tough balance to strike and I won’t pretend to be an expert on it, I’m only just getting started myself.

The thing is the vast majority of people find living to be on the whole a source of great joy, far greater than any suffering they may experience as a byproduct of it. The handful who don't do have the option, grim as it may be to consider, of returning to nonexistence. The fact that this option isn't taken by even 1% of people suggests strongly that nonexistence just isn't that compelling an alternative.

The point is that the obligation flows one way because one party was inserted into it without their consent.

Does their lack of preexistence impact that equation in a meaningful way?

Yes. Obviously.

Well, philosophically it's not a big problem, because dissatisfied can very easily stop participating.