Is NFP not a type of contraception, in a way?
No.
NFP is information. Based on this information you decide to have intercourse or not have intercourse, depending on whether you want to achieve or avoid pregnancy. (this is often overlooked, but NFP is used to ACHIEVE as well as AVOID pregnancy.)
Deciding not to have intercourse isn’t contraception, it is respecting God’s design for marital relations.
Contraception is an action whereby you engage in intercourse and try to thwart its natural outcome by a device or an action before, during, or after intercourse. You seek to have relations and you disorder the relations.
In NFP, you refrain from relations.
They are not the same, morally. Both are means to the end of spacing/avoiding children. One is a moral means (refraining from relations periodically) and one is an immoral means (contraception). Means and ends are not the same thing, and the morality of an act depends on the three fonts of morality all being moral-- intention, object, and circumstances together. While contraception and refraining from relations periodically both have the end of avoiding, they are not the same means of avoiding.
If one actively monitors their cycle, temperature, mucus etc etc so thoroughly, in the hope they won’t conceive… that is not being open to life?
That isn’t what the Church requires of us, although it is often stated that way. There is no teaching about a vague “openness to life”. What the Church actually teaches is that
each act of intercourse must be per se (objectively, by its nature) ordered to both unity and procreation. Meaning, it is an unaltered act of intercourse. So, when you contracept, your marital relations are disordered (i.e. NOT ordered to procreation and unity of spouses). When you refrain from intercourse, you aren’t disordering anything because you aren’t having intercourse. When you DO engage in intercourse, you aren’t disordering the act in any way. It’s a natural, completed act of intercourse just as God designed it. God designed the infertile periods of the cycle. God designed menopause. God designed a woman to not be able to get pregnant while already pregnant. And in each of these situations where the woman is subjectively infertile at that moment, marital relations are still good, holy, and morally ordered because the couple hasn’t taken any action to disorder them. (This is
also why disordered acts that replace intercourse are STILL immoral even when a woman is pregnant, sterile, post-menopausal, etc.)
How is that any ‘better’ than using a barrier method of contraception?
Because one is pleasing to God: periodic (or complete) continence
And one is displeasing to God: contraception