Many things can be true at the same time. Howard didn’t deserve to have his reputation ruined, but Jimmy and Kim hating him didn’t exactly come out of left field.
Howard is a smart, strong, and respectful guy who is easily manipulated by Chuck. Howard, on orders from Chuck, treats Jimmy and Kim like garbage early on in the show. Howard always liked Jimmy, but would help sabotage his career because Chuck was a jealous big brother. Howard was always looking out for the best interests of the firm, unless Chuck had other petty interests. He was Chucks lapdog, and it’s understandable why Jimmy would dislike him.
Howard was also really harsh to Kim early on. He punishes her for losing the idiot Kettlemans to no fault of her own. She, and HHM, got them a great deal, and they blew it up because they were stupid. But because they were a big client, and left HHM, Howard punishes Kim, and sends her to doc review. He does the same after Jimmy pulls some slippin shit with Davis and Main. Ofc, a lot of his poor treatment of Kim came from Chuck. But even when Chuck lightens up on Kim, Howard still insists she remains in the dog house.
Howard tries to get Jimmy disbarred. He tried very hard to achieve chucks goal in ruining jimmy’s career. Sure, Jimmy deserved to be disbarred, but as far as he and Kim are concerned, Howard did his part in ruining Jimmy’s career, all because Chuck hated his brother.
Howard hardly ever stood up for what he believed in. But to his credit, he did try to atone for his mistakes. That said, it’s understandable why Kim and Jimmy didn’t like him. He kept them down. Excusing Howard for being an asshole because he looked up to Chuck is a shitty excuse. He didn’t deserve his fate. Jimmy and Kim went way too far. But it’s not really fair to judge Kim and Jimmy for their dislike of him.