I wish Johnson got more media coverage and had been allowed into the debate. Sure, it looks bad when you have gaffes like those, but it's a lot worse when those are just about the only thing most people see of him. Remember Trump and his (maybe) mocking of a disabled man? Even if that isn't what he was doing, he certainly looked foolish. What about Clinton with her wide-eyed jerking back of her head when that group of reporters was asking her questions outside a coffee shop (I think that's where it was)? Either of those are at least as silly as Johnson's saying he could win a debate with his tongue between his teeth.
Johnson doesn't have the many, many scandals that surround both Trump and Clinton. He doesn't have a history of screwing things up while in government nor, that I know of, as a businessman.
I still think Weld might have made a better face for the candidacy, and I agree that Johnson hurt himself with these mistakes, but I don't understand how they are worse, or even on par, with all we've seen and read about Trump and Clinton.