My guild is currently doing 16 man hardmode content, up from 8 man hardmode. I prefer 8 players because at least then you know everyone in the group. The more often you group with them, the better you get to know them and their playstyle. This is obvious, but it's harder to organize 16 people to log on than it is for 8. Also, a bigger group usually means you're carrying a few baddies with low awareness. Loot takes longer to pass out, people tend to AFK more between boss pulls, and sometimes people come and go as they please. The only good thing I've noticed about 16 man is that clearing to bosses feels faster.
At least with 8 players, you can have an easier time scheduling or rescheduling operations.
bosses are easier on 16 men, your argument is invalid.