Grateful? When has Trump ever been grateful or expressed being grateful about anything? Nothing is ever good enough which is reason #2345 why he needs to be defeated this year and kicked to the curb with his cronies along side him.
Barr is a crony of Trump and no hero at all. He desparately wants to do Trump's bidding and has been for nearly a year quietly, but Trump, since having his misconduct approved by the Senate, has lost all control in his endless quest to grab power and abuse his office. He is saying out loud what he & Barr have been up to and taking credit for it. He does not understand what they have done and believes he has unlimited authority.
Barr shares his belief in outlandish executive power that has little basis in the law or Constitution. Remember, Barr auditioned for the job by sending an unsolicited memo to the DOJ & White House denouncing Mueller's Russian investigation - Trump knew nothing about and had never met Barr before that time, but because of his desire to have a Roy Cohn type as AG instead of Jeff Sessions (who followed the law and protocol by recusing himself), he orchestrated the firing of Sessions, the placeholder Whitaker and then, when the time was right, installed Barr.
Barr's first order of business was distorting and blunting Mueller's findings and report. This was a direct threat to Trump (and the executive branch) that must be stopped. Barr knew he could not outright fire Mueller even though Trump had tried multiple times to do so, but had been stopped by his own White House Counsel, Don McGahn, or the people he ordered to act had not followed through since they knew it was obstruction of justice.
Barr did his public press conference where he communicated the distorted version of the Mueller findings, stressing that no conspiracy with the Russians had been proven and that Mueller, following the DOJ protocol that a sitting President cannot be indicted, had left any criminal referral decision to the AG. Somehow, the 10 fully documented instances of obstruction of justice were not mentioned nor was the evidence Mueller found of coordination between Russians, the Trump campaign and Wikileaks during the 2016 election. Barr also conveniently ignored Mueller's recommendation that the finding summaries his team had prepared be released to the public (we still have not seen them) and then delayed the release of the report for several weeks under the claim they were being "checked" for needed redactions. Mueller's team of course had already done this in coordination with DOJ, but Barr wanted his narrative to control the media coverage and allow Trump to make sure his base believed it was "total exoneration" for him and proven as the witch hunt he had always claimed.
Once the Mueller findings were effectively distorted, the report's release and Mueller's subsequent testimony naturally landed with little impact as the Republicans already had their talking points and enough smoke had been created to ensure the American public would either not trust it or be unable to really decipher what the truth was. .
That has been the hallmark of Barr's tenure besides, of course, the political interference on behalf of Trump's cronies and against his perceived enemies that Barr has engineered. The Flynn and Stone sentence reductions, the Flynn case being "reviewed" by a team of Barr selected prosecutors, the phony Huber investigation into Clinton (again!) which found nothing, the Comey investigation which found nothing, the bogus Durham investigation, the attacks on the IG report by Barr and Durham that found no evidence of "spying" or "treason" or wiretapping of Trump Tower" or the other nonsense Trump and his sycophants had claimed for years.
Barr is being exposed for what he is which is a good thing. If he truly cared about the independence and integrity of the DOJ and believed that Trump's tweeting made it impossible for him to do his job, then he would resign. He will never resign because all he really wants is for Trump to shut up and stop telling the world they both are corrupt.