Right. Still it's not, in terms of numbers, the MOST COMMON status - and yes, this is the reason "we are still here". Try to procreate with exclusively homosexuals relations, let me know if it works for you.
I don't see your point here. Gender and relationship diversity is well documented to be pro-fitness across a broad range of situations. Why is it so important to you to qualify "common and perfectly normal" with "but still less than 51% statistically!" Who cares?
And as far as reproduction and child care it turns out that adults without their own direct offspring involve themselves in caring for community offspring in varying degrees right up to full fledged adoption of "surplus" or orphaned young in lots of different species. If you don't think that's pro-survival then my son would like to have a word with you.
Please remember that the ultimate instict of every living being is to procreate. Survival instincts above all.
Yeah, so we thought back in the 1950s. Then along came George C. Williams and the idea of gene-centred evolution.
But, regardless of that, while "reproduction" is clearly the simplistic "goal" of any living thing, the mechanisms of that reproduction are not always simple. Mechanisms and behaviours are direct, not goal oriented. Animals want to "do reproductive stuff", not necessarily reproduce. Even mechanisms and behaviours that evolved to improve direct reproductive success are open to "subversion". When you evolve permanent pair-bonds you can easily end up with some members of the species forming non-reproductive permanent bonds. Or dogs humping the furniture.
You've also got to remember that "survival instincts" are much, much more complex than you suggest, especially in humans. People die trying to save the children of strangers. Soldiers die for their country. People die for their religion, or ideology or bungie jumping....