A UK court found her sufficiently credible that she won her libel suit against him there, which is no joke considering how easy it is to win a case accusing someone else of libel in the UK. We have audio of her saying she was afraid he was going to kill her and him not refuting it, which is a pretty tacit admission that she had some reason to think that. We have texts from his assistant saying she told Depp that he hit Heard while blacked out or in a rage.
However credible or otherwise you find her claims, whether or not you believe that she was also abusing him or that she was just reacting to his abuse, there’s not a credible argument to be made that he didn’t abuse her.