I would like to protect my proposal for famous architects. It is similar in character to the one about famous painters and certainly adds to our understanding of the sites. There aren't enough such artists who have 3 or more whs and yet I suppose we can learn about the history of architecture through such a connection of architects who only have one site on the list. Palladio indeed has his own category, but it is not dedicated to his work solely but to others who imitated his style as well.
Maybe this proposal can be rescued if we stress what exactly the intended monuments are (if they are not the entire site already).
I don't remember my list exactly but I try:
Last Supper - Bramante
Acropolis - Phydeas
Tugendhat - Van der Mies
Palau de la Musica and San Pau
Vatican - San Petro, Bernini
Rome - Musei Capitolini, Michaelangelo
Vicenza - Villa Rotonda and other, Palladio
Wuerzburg - Balthasar Neumann
Vienna - Otto Wagner (Postsparkasse, Secession), Loos (Loos House, American Bar)
These are all important architects in the development of Western art. I don't remember if I suggested others as well, but I think these do earn a connection.