The EBV6 is the only engine in the expo/navi. So yes, it is the biggest volume seller by default.
You can deny it all you want. People aren't buying the expo/navi in droves as expected and one of the reasons why, is in a 3+ton brick, when you plunk down the coin you are for one of these and then plan to keep it 20 years, consumers don't want an TTV6. Those other vehicles mentioned have different target demos and different uses/applications, different consumer ownership lifespans, etc.. Again, sales tell the tale.
The 5.0 is only 25% of the take rate of the F-150, so little they've cut production because the demand on the EcoBoost is so high