So, federal courts flat-out do not have jurisdiction over congressional impeachment proceedings.

No shit sherlock. But what they do have is power over disagreements between the Executive Branch and the Legislative. Disagreements such as whether or not something qualifies for Executive Privilege.

A fact that shuts down your baseless and unsubstantiated claim (aka a lie) that the impeachment process increases Congress's power.

but the courts have defined and limited Congress' implied (not textual) investigative/oversight power.

None of those restrictions apply to your claim that impeachment increase Congressional power. They are irrelevant to our conversation about your claim that the impeachment process increases Congressional power.

You're arguing a straw-man that has nothing to do with your claim. Continuing this conversation is a waste of my time.

Have a good day.