It is honestly always a hard choice when the 2H has much higher stats and item level, but it really comes down to the fact that we scale with our weapon damage and dual wield gives us the benefit of double-proccing Dancing Steel (amongst other things). Early on, when RPPM trinkets scaled with weapon speed, we did see MAJOR benefit in 2H - but unfortunately, that did not go live, and so a very, very slight delta still exists between DW and 2H.
Note, however, that in current tier - with Heroic Thunderforged and several different item levels, it is not going to be uncommon for a 2H to outperform DW. That is the problem with having a tier in which weapons with a 19 item level difference can drop - it will complicate things for you.