LOL! That's good that you have confidence of parental love. I think my mom loves my eldest sister the most to the point where I make jokes about it. My thoughts aren't because of anything i've felt but because of a conversation that I overheard. I overheard my mom (or maybe her sister?) saying that it is impossible to love your second and third the same as your first because you have so much more time to spend with the first.

I have seen evidence of the first not being loved the most in families. The funniest family to me is one where the mom CLEARLY favors the middle child. I think the child was sick as a baby and woke up a "mama bear" instinct in the mom, but really Im just speculating, I don't know why she favors the middle child so. Its just clear that she does.

I think 90% is high estimate for instant love. That would make 90% of people capable of deep parental love, and I just don't see evidence of that in society.