In the theory way I agree this is possibly the best way to do things.
However, Life is very rarely that simple. For example, I met DH (then DP) and fell pregnant 8 weeks into our relationship. Not something I had ever done up to that point in my (then) 27 years. We agreed after a week of thinking through all eventualities, that we would give it a go and keep the baby.
However as it turned out DH a year a bit later, when DS was nine months old, developed stage four cancer, and the chemo he was on resulted in him being infertile.
A year and a half later after battling cancer, dementia, death in the family and other illnesses we tied the knot in front of 50 close family and friends, three years after meeting.
Had we not kept the pregnancy, and waited even half the time you are suggesting, we wouldn't of being able to have any. And being a mother was the only thing I had ever really, truly wanted.
So six and two threes, and all of that. In theory YANBU, in real life I think you are beinga bit. Circumstances dictate more than theory.