You're making an argument based on semantics, not factual evidence. Essentially, you're saying Barr says there's no crime, so there's no evidence of a crime. As if the evidence disappears and appears according to one's opinion of whether a crime occurred.
William Barr's expressed opinion is an "opinion" on the matter as follows,
“ the evidence developed by the special counsel is not sufficient to establish that the president committed an obstruction-of-justice offense.”
This was Mueller's stated "opinion" on that same evidence:
“If we had confidence after a thorough investigation of the facts that the president clearly did not commit obstruction of justice, we would so state,” Mr. Mueller wrote. “Based on the facts and the applicable legal standards, however, we are unable to reach that judgment.
The evidence we obtained about the president’s actions and intent presents difficult issues that prevent us from conclusively determining that no criminal conduct occurred.”
Here is Barr's argument of why he feels the evidence does not fulfill the requirement of corrupt intent to substantiate obstruction:
"And as the Special Counsel’s report acknowledges, there is substantial evidence to show that the President was frustrated and angered by a sincere belief that the investigation was undermining his presidency, propelled by his political opponents, and fueled by illegal leaks. Nonetheless, the White House fully cooperated with the Special Counsel’s investigation, providing unfettered access to campaign and White House documents, directing senior aides to testify freely, and asserting no privilege claims. And at the same time, the President took no act that in fact deprived the Special Counsel of the documents and witnesses necessary to complete his investigation. Apart from whether the acts were obstructive,
this evidence of non-corrupt motives weighs heavily against any allegation that the President had a corrupt intent to obstruct the investigation".
Above, we see that Barr cites the evidence of "non-corrupt" motives. To wit, that
Trump co-operated fully and that Trump was under a sincere belief that
"the investigation was undermining his presidency, propelled by his political opponents, and fueled by illegal leaks".
To Barr's claim of Trump co-operating fully, we know that this is only partly true. For one thing Mueller's team was trying to get a meeting to question the President about it, but he would not agree to be questioned. Mueller:
"During the course of our discussions the president did agree to answer written questions on certain Russian related topics, and he provided us with answers. He did not similarly agree to provide written answers to questions on obstruction topics or questions on events during the transition.
Another issue is Barr's claim of Trump not asserting privilege claims. Since Trump had talked repeatedly in public about Comey, and denied Comey's claims of Trump seeking loyalty and being asked to let Flynn go, it's doubtful what claims of executive privilege could be claimed. But as I understand it there were in fact claims of privilege pertaining to documents about Comey's firing which required a subpoena.
So that leaves us with this motive for firing Comey and attempting to fire Mueller;
"The sincere belief the investigation was undermining his presidency, propelled by his political opponents, and fueled by illegal leaks".
So in Barr's opinion, it is a "non-corrupt motive" to first fire Comey and attempt to fire the special counsel if the President sincerely believes the investigation is undermining his presidency, propelled by his opponents, and fueled by illegal leaks. Note that the President just has to believe these things, regardless of whether they're factually true or untrue. So according to Barr, if the president hadn't believed these things, then there would be no proper motive for firing the special counsel found in the report, even though the investigation included the exposing of Russia's influence to help Trump win, which Trump claimed at the time was a hoax invented by Democrats and the media.
Here are some other opinions of the evidence in Mueller's report. From lawfare:
