The trash is the only thing that is harder on 16 man. The bosses themselves are no more challenging. Pylon boss may be more challenging, but P2 + P3 SOA mechanics favor 16 man. Additionally, there is no incentive to ever do 16 man. Why bother getting 16 of us together instead of splitting into 2 8 man's and getting the exact same loot?
To the OP: Also using "2 pieces of loot in 40 man's in WoW" is a pretty stupid argument, seeing as how 10 man raids dropped 3 pieces in the later stages of WoW. Do you gear extremely quickly in this game? Sure. There are still a minimal amount of people walking around in full Rakata.
WoW was famous for becoming a welfare epic game. I don't see why this is an issue in SWTOR.