It really isn't.
An ad hominem attack is not quite as weak as name-calling. It might actually carry some weight. For example, if a Boris Johnson wrote an article saying MP salaries should be increased, you could respond "Of course he would say that. He's an MP."
That wouldn't refute his argument, but it is at least relevant.
(, Fri 17 Aug 2018, 16:04, Reply)
Name calling is a form of ad hominem.
And is probably the weakest form.
(, Fri 17 Aug 2018, 18:28, Reply)