I can't knock the six cylinders with boost. We bought my wife a F150 in 2015 with the 3.5 ecoboost with 7,200 miles on it. We still have it; it now has 157,000 miles on it and still looks great. I have been very happy with the ecoboost, it tows well and has a great right peddle reaction. Just standard maintenance and wear parts. At 150,000 miles I replaced plugs, coils, o2 censors, and an evap valve and just put a new set of tires on it last weekend. After the new tires my wife even commented how the truck still feels and drives like it did in 2015.
The drive for smaller CI in 1/2 ton trucks has to be related to EPA regulations, meanwhile the 3/4 and 1 ton trucks (which do not fall under the same regulations as 1/2tn) are getting bigger engines.