You agree that impeachment and indictment aren't the same thing. It's the basis for you finding that a superior Officer can't be indicted, and can only be impeached. Indictment is the "accusation power" of the executive; impeachment is the "accusation power" of the House.
We agree that only the House can impeach.
Our disagreements are over whether or not the executive can remove a superior officer, and whether or not the executive can investigate and indict a superior officer.
Another way to say that is that we disagree over whether the House and executive have concurrent powers of accusation against superior officers. You find that they do not, that the House power to impeach precludes the executive power to indict; and precludes the executive power to investigate crimes.
If impeachment and indictment were the same thing (that is, if the two terms were literally synonyms), then the executive could impeach, and the House could indict. Obviously that isn't the case, see constitution giving sole power of impeachment to the House, and the duty to faithfully execute the laws to the executive.
Differing opinions are fine especially if they are supportable, but when it comes to the feds, the basis for a valid argument is the Constitution as written and originally understood and intended. It is that constitutionally-based rationale where I find my disagreement with you.