“Immaterial.”
Well, it’s pretty material that Podesta couldn’t possibly have been talking about “the leaker”, as you asserted.
“Podesta himself gives a plausible motive for killing leakers and taking that risk.”
Except the email chain wasn’t talking about killing anyone, it was talking about rescinding job offers to potential hires that were found to be leaking, and telling other potential hires that those would the consequences. Podesta wasn’t even the one proposing it, he just agreed with the recommendation.