That's precisely what I've been thinking/saying. I think there are reasons why Sam is Lucifer's choosen vessel. One of which I think is their shared affinity of self importance. I'm not saying Sam has an inflated ego, but he can be self absorbed, sometimes unconsciously, other times purposefully.

I wonder if the writers didn't leave Sam the way he is on purpose here. I still steadfastly believe Sam will not turn dark, but as long as the character trait is there, Sam has a weakness, and the danger he might succumb to Lucifer one day is alive. Hence more drama and angst.