I would put W in the bottom five, along with LBJ (whose Great Society, initiation of the Vietnam War based on false pretenses cooked up by Rob’t. McNamara and 1965 Immigration Act did incalculable damage); Obama (pushed state socialism); Buchanan (fiddled while the Civil War brewed); and Franklin Pierce (a drunk). W needlessly started a war that too many families had to pay the ultimate price for, that accomplished nothing, and that cost trillions in dollars. He was and is a congenital idiot.
I cut Pierce some slack for one enormous reason: His young son was killed in front of his eyes in a train wreck before his swearing-in. Both he and his wife were suffering from shock and depression for the entirety of his administration (his wife almost never came out of her room at the WH). Mrs. Pierce believe the child’s death was the hand of Providence for her husband having run for the Presidency. More pitiable than incompetent.
His successor Buchanan couldn’t have done anything, either, to prevent what was coming. To his credit, at least he mobilized the Union in the last months of his term and tried to purge pro-Southern interests in his administration (although probably too late by then). Still, he was in an untenable position.
I agree about LBJ being a fiasco (willfully so) and Dubya has moved down in my estimation as well. He all but handed the keys of Congress to Pelosi and Co., and also did nothing to stop Zero, who was a clear and present threat to national security. He and his classless family issuing a de facto endorsement (with the daughters support outright) of Hillary in 2016 was the last straw. Elevating GHW Bush was Reagan’s greatest error in judgment.