always found max hp/max atk to be better than max hp/max def on the listed set becausethe additional atk evs provide far more utility than the defensive investment - CB Terrakion is 2HKOing with CC regardless and the defensive spread coming in on SE is only 'countering' him in a loose sense of the word since it hasn't really granted you any momentum whatsoever unless you have something worth spinning away. max atk still counters things like Tyranitar just as effectively but actually does something once it's in. it can provide a bit of muscle because Close Combat/Stone Edge off of 317 Atk stings like a bitch doing neat stuff to semi-bulky Pokemon such as Keldeo (68% max as opposed to 49%) and Thundurus-T (102% max as opposed to 73%).
you often go on about how pitifully weak he is but that is not an inherent trait of hitmontop, it's just a component of that EV spread. max hp/max atk is a far better addition to any balanced team in my experience. max def just forces things out a few times, gets worn down in the process and utterly kills your momentum.
with that in mind, hjk is probably a better AC option than low kick because it gives you a odds-on chance to ohko breloom after SR but doesnt offer too much else.