Hello!
In your eyes Nami might be total support, but when i tried do build and play with her as APC, she somehow did dissent damage and she kept on with team. In early game with good bot lane teammate she can be very strong and with barrier she can be safe. In mid and late game she can realy help team with ult, as well as take kills and assists.
As you see build, masteries, runes are based on damage and aggresive gametype. Build is just testing prototype be it worked for me. Renember! - your build and gameplay is based on enemy nad your team as well! - Try this type of Nami while shes free.
Rate and keep good atetude.
Sorry for any grm. misstakes. I`m just learning english.