I think there's no right or wrong answer to that. It's going to vary greatly from country to country, depending on its population, demographic needs and wants, and various cultural factors. Ireland might need or want a very generous implementation of jus sanguinis, for reasons which aren't at all relevant to the US (for example).
Surely, if you know your history, the Irish diaspora is huge. So many had to flee famine, unemployment and persecution. The automatic right to Irish citizenship
jus sanguinis of grandparents is an acknowledgement that people left the country they loved because they had no other option.
Jus sanguinis is a reflection of ancient tribalism going back at least a thousand years in European history, and beyond. Many countries today are an amalgamation of various tribes all joined together by a wider boundary. For Example, Sweden used to be just that region called Svea (hence its name Sverige); Finland as part of the Swedish empire for over 700 years was just the bit below the Nöteberg line - north belonged to the Novogoradians. The Muscovites and the Novgorodians used to be two distinct peoples. As did the Saamis across the Arctic, now subsumed by the boundaries of Russia, Finland, Sweden and Norway.
The USA being a lot younger, heavy migration from Europe from about the mid-1600's, and then only on the east coast side (Virginia, for example). The Dutch nabbed New York, the Swedes predominated Delaware, the French the deep south, Scots and Irish bonded servants, too. It is little wonder
jus soli would predominate in the USA, given its lack of any real ancient culture, other than the Native Americans, and even they were/are highly tribal.
Then there was religion defining nationality. At some quite recent point in history, you could not obtain citizenship unless you were a Christian (this kept out Jews and Muslims as late as 1897 in Norway, for example). The Jewish religion was even barred in the UK, with people having to practice it underground. That barrier has now come down. But there is a long way to go before the tribal ones come down to just j
us soli, and to heck where grandpa hailed from.
I wouldn't be surprised if a couple of hundred years from now, Europe will be just one country, and today's countries little more than its counties. (Heaven forfend!)