I agree that Trump should be allowed to go to the court with legit arguments about why he should be able to defy subpoena's, but when the arguments reach the level of Silly, its obstruction.
Trump is arguing in court that he has absolute immunity from investigation, that is simply silly. The Constitution requires the Congress to conduct oversight.
I don't know how impeachment works, but in civil court a party issues a subpoena and then the onus is on the recipient to obtain a protective order otherwise they must comply
with relevant or those reasonably calculated to lead to admissible evidence requests for docs and rogs and admissions etc...