Okay, so I think I see where you're getting yourself into trouble.
Subpoenas are
not limited to the Courts. The Legislative and Executive Branches issue
administrative subpoenas and
Congressional subpoenas that carry the same basic weight but without the judicial oversight. That's why you hear members of Congressional Committees talking about subpoenaing the Executive Branch, for example. It's also why the DOJ (and some of its composite agencies) are able to issue subpoenas during their investigations. (The FBI is the notable example here)
The vast majority of your argument falls to pieces at that point. The first four points you made are invalidated by this fact.