Peter Abernathy doesn't have the data that Delos wants. It's in Bernard, which is why he's malfunctioning. Why would Bernard make the perfect decoy? Because Peter Abernathy is Delores' dad. In a more non-robotic way, so is Bernard.
Why I could be wrong: Her dad got replaced because he started malfunctioning after seeing the pic of the real world (almost a more advanced signs of symptoms bernard was showing), and we have no idea where the original is. Also, I missed Bernard repairing himself on the first viewing. But.... I'd like to think the Hosts are a bit more sturdy than to start leaking fluid and malfunctioning from a single hit.
I also wanted security dude everyone was so happy about to turn out to be an older Logan.
But his name's not Logan, so ignore that entirely.