I understand that in theory but what is to stop an impeached president from citing this decision as the reason why an impeachment is not valid? I guess I’m asking the extent to which this muddies the waters of the remedy.
The Impeachment is valid because it exists outside the "legal/illegal" framework; and isn't criminal in nature.
What this does do is create a defense of "it must have been an 'official duty' because I wasn't impeached, and convicted, for it".