I would not think of the 3.5 EcoBoost V-6 as a drawback. It’s a major improvement over the old Triton V-8.
The 3.5 EcoBoost V-6 that will be going into the 2015 Expedition is same one used in the F-150 (its actually the premium engine offered in the F-150) and the same one that was used in the Vegas to Reno off-road race (which it won), Baja 1000, and Tecate 1000 endurance off-road races. All of which were successful.
Now more than ever, people are opting for V-6s over their V-8 counterparts in the full-size F-150. Sales of V-8 F-150s are down compared to V-6 F-150s. All told, V-6 engines now make up well over 50 percent of all F-150 sales.
The 430 lb-ft of torque the 3.5 EcoBoost V-6 makes will allow the Expedition to outclass its rivals in towing capability. 90 percent of that 430 lb-ft is available at just 1,700 rpm, and all 100 percent of it is available all the way to 5,000 rpm. It has a very "diesel-like" torque range.
3.5 EcoBoost V-6 torque output vs. others (in greatest to least):
2015 Ford Expedition .............. 3.5 EcoBoost V-6 ........... 370 horsepower, 430 lb-ft of torque
2015 Mercedes-Benz GL 450 .... 4.6 BiTurbo V-8 .............. 362 horsepower, 406 lb-ft of torque
2015 Toyota Sequoia .............. 5.7 i-FORCE V-8 ............. 381 horsepower, 401 lb-ft of torque
2015 Dodge Durango ............... 5.7 HEMI V-8 ................. 360 horsepower, 390 lb-ft of torque
2015 Nissan Armada ................ 5.6 VK56DE V-8 ............. 317 horsepower, 385 lb-ft of torque
2015 Chevrolet Tahoe .............. 5.3 EcoTec3 V-8 ........... 355 horsepower, 383 lb-ft of torque
2014 Ford Expedition ............... 5.4 Triton V-8 ............... 310 horsepower, 365 lb-ft of torque