He also said that with no underlying crime to give direct intent required for obstruction there is no way to prove obstruction in court.

Not quite. Barr himself said in the senate testimony yesterday that there does not need to be an underlying crime in order to satisfy obstruction of justice charges. It's that customarily when someone is charged with obstruction of justice they tie in the underlying crime related to the obstruction. In this case the president did attempt to obstruct the investigation. Whether or not there was an underlying crime doesn't change that. If you can find me a statute that states there must absolutely be an underlying crime in order to charge obstruction then I will be glad to take a look but so far I can't find anything in the statutes that states this claim.

It's not too dissimilar from a simple vehicle search. There are many cases in which a vehicle is searched for drugs when an officer claims probable cause and nothing is found and people go on their way. Do you feel that people should be allowed to obstruct the search (which absolutely qualifies as obstruction of justice) even though they know they are innocent?