Your argument is a non sequitur. You are saying in essence: "Someone, somewhere, under totally different circumstances was not prosecuted. Therefore, this particular prosecution is selective prosecution, and therefore inappropriate." By that logic, we should just stop prosecuting crimes altogether, on the logic that we are unable to prosecute all crimes consistently.
There wasn't an argument per se, but an attempt to point out a possibly, similarly politically-influenced miscarriage of justice.
It may be a non sequitur to suggest that the pardon of one convicted financial criminal is similar to the lack of convictions in another likely financial crime context, but it seemed germane and parallel to me.