Maybe you should have a look at roman successions, even if they were generally adopting relativelly close relatives.
Paternity is a social construct.
There are cultures where paternity simply is not important. In a matriachal society, a person's mother's brother is apt to be more important than a biological father, sometime to the point of not knowing who the father is (because it is unimportant).
Paternity is an objective biological relationship as well as a social construct. Just because paternity can be a social construct does not mean that all other socially constructed alternatives are equally useful, or can even lead to a stable society. The mere fact that the traditional Western concept of paternity has been around for hundreds of years means that it hasn't led to our degeneration or destruction and at the very least is compatible with a productive society.
The fact that most notions of paternity are almost universal means that there is something fundamental driving this which can only be overridden in a handful of cultures. Perhaps there is some instinctual male drive to be more invested in their genetic offspring. Investing in their own genetic offspring increases their biological fitness and makes them more likely to pass on their traits of favoritism. Perhaps in cultures that don't have these widely held traditions around paternity aren't able to secure paternal investment and encourage long term monogamous relationships, which leads to the culture's destruction, degeneration, or stagnation.
I suggest to refine this statement, because as written, it posits
the biological and social parts of reproduction as equals.
This is slightly misleading since the basic biological facts of reproduction have not been modifiable so far in human history. Reproduction has always needed a fertile man and a fertile women having sexual intercourse. (Note this may change in the future with technological advancement, e.g. cloning and artificial wombs.) In contrast, the social aspects of reproduction have been varying a great deal on the surface.
I'd rather say that the social rules, rituals, taboos, institutions, all emerge and stabilise in order to give structure to and make predictable the underlying biological facts of reproduction. Note that
reproduction is humanity's the single most important task.
Giving predictable, teachable and learnable social structure to reproduction has been all the more important before humanity started worked out how reproduction works and began to be able to control it at will (genetics, contraception etc). It is not surprising that there is a great deal of surface variety of social overgrowth on top of the basal biology, since genetics is rather complicated (and not fully understood as of June 2019, e.g. epigenetics) and has a lot of randomness built in. Moreover, reproduction, being the single most important task of humanity, intersects with all manner of other social institutions. This has encouraged the ad-hoc theorising, and overfitting on anecdotes that became enshrined as social institutions.
Summary: the social aspects of reproduction have been humanity's attempts to understand, manage and control reproduction, and are a reaction to the biological complexities of reproduction.
Royal intermarriage has been practiced by ruling dynasties since times immemorial. It had often been observed that this leads to problems and infertility, and indeed this is the root cause for the incest taboos that you find in varying forms and shapes in most cultures and religions. However, it has only been with the rise of modern biology and genetics in the 20th century, that this practice was abandoned.
Speaking of Ancient Rome, it has been speculated that the decline of the Roman Empire was in parts caused by the failure of the ruling families to produce enough children. Naturally, we don't have enough information today to confirm or disprove such speculation.
I have no idea why you link to an article about the Mosuo. It has no bearing on the biological nature of paternity.
Paternity is a social construct.
There are cultures where paternity simply is not important. In a matriachal society, a person's mother's brother is apt to be more important than a biological father, sometime to the point of not knowing who the father is (because it is unimportant).
https://www.spiegel.de/international/zeitgeist/the-mosuo-mat...