: And finally I feel there's a further balance in that in the second Age there exists one Feanorian (Celebrimbor), one Fingolfian (Gil-Galad) and one Finarfian (Galadriel)...

Says who? Elrond is descended from them as is Celebrian, and Amroth if you take him as Galadriels son.
Maglor, Caranthir and Curufuin were all married, an Chris Tolkein himself reports that his father said 'we never meet the progeny of Feanors sons' whilst debating the parentage of Celebrimbor.
There could feasibly exist other offspring who do not enter the tales but nonetheless exist
Don Q