I have a suggestion for how family tree should looks like if the partner was 2nd cousin, 3rd cousin and so on....
instead of duplicating partner with same ancestors, why don't we just connect their line together and continue the tree instead of duplicating the tree with the same ancestors.
Theoretically in your screenshot you are perfectly right.
Anyway you are perfectly right that duplication of branches are a
shame.
I am working on it.
I agree with you. I think you also need to make it work on 1st cousin too.