Yes, if you believe political investigations are a valid maneuver, then this validates the House's vote for impeachment regardless of the fact that it's a valid inquiry on legal grounds alone due to the President's admission of the transcript.
As for the request that Democrats made for Ukraine to cooperate with the Mueller probe, that is a separate issue and I would hardly call it dirt unless the investigation turned up evidence of Trump's wrongdoing, which you claim he is innocent. Investigations are not always about turning up dirt. Sometimes, investigations lead to absolution.
I guess Trump is unique in that investigations are incapable of absolving him of criminal wrongdoings.