I read the linked article and didn't see anything about Catholic teaching at all. I'm at a loss as what the so-called "success sequence" Walther proposes even is. He may be a Catholic writer, but I don't think he's actually writing a Catholic piece here. So I'm not sure how the article is connected. I'm therefore going to ignore the article and focus on your question! Note: no punches pulled.
I don't think these two banner concepts, sex outside of marriage and child murder are directly comparable, though both are surely connected with the theology of the body. This stems from the idea that every human is made in the likeness and image of the Creator, that the Creator deigned to be born into his own creation as a human being and that as a creation of God, the human body deserves respect & dignity as it is part of the human person.
Contraception. Obviously, any kind of contraceptive that actively kills a baby -- a tiny human person -- is going to be frowned upon by Church teaching, simply because that is an act of murder. It eliminates an innocent life and that's always a no-no. Also, contraception that doesn't directly kill a baby, but simply prevents the baby from happening has knock-on effects, namely that of objectifying one or the other sex partners. For every kind of sexual life form, humans included, sex has a couple purposes, the primary of which is making more humans. Once you take the primary purpose away, the creation of a new living being, you're left with the less noble purposes: bonding, having fun. The knock-on effect of such responsibility-free sex is that it can lead to promiscuity. Hey, if I can get off on the missus without worrying about having a kid, why not get off on the cute coworker as well? You know, spice things up a little!
Fornication. Procreation becomes intimate bonding becomes fornication becomes friends with benefits. This is just another way of saying "I'm using you for my own pleasure, and I'm okay with you using me for the same reason." Theology of body speaks about the divine aspect of the body, as the temple of the Holy Spirit, and the act of banging a girl without being married to her rather disrespects her humanity as divine temple. Marriage, obviously, is the sacred union of a male and a female into a single new entity, the sacramental family, and is ordered towards the making of new people. Sex that is thus disordered is sinful, not because sex is bad or because Catholics are prudes, but simply because fornication is an abuse of human dignity. It dehumanises people and makes them into objects for the use others.
Which is Worse? There are different magnitudes of sin, certainly. While no sin is ever really all that great to have on your heart, some are worse in degree than others. It's obvious that depriving a person of their life is a really bad sin. Really grave. Is it worse than robbing a rich celebrity? Or embezzling squillions of dollars from a major corporation? I think it is, even if that person is a microscopic speck comprising four cells. US law might tell us that embezzling jillions is a worse crime than stealing a fifty thousand dollar bracelet; but I'd argue that stealing a panhandler's jar of change is far worse than both.
So: while obviously contraceptive use that kills a baby within marriage is worse than unmarried sex where a baby can at least happen; neither unmarried sex in and of itself nor killing a person are good things to aspire to. The reality is that the Church doesn't teach that one particular sin is worse than another particular sin. There's no menu listing how bad each sin is --- the wages of sin is death. Not physical death, but spiritual death.
- Contraception, Sterilisation and Abortion
- Theology of the Body