what makes you say this? he's got an insane am record. he's fought so many times there's not gonna be anything he's not come up against only person i can see giving him trouble is Sergey (and vice versa)
At one point earlier in the fight Johnson haulted Beterbiev's come forward aggression briefly with a nice body shot. Kovalev with that long reach would do well to touch that body up with those hard straight shots he throws.
Johnson was a southpaw and Beterbiev prepared for an orthodox fighter. Gave him some rounds and it's something he needs.