Double Punch simply isn’t the best skill for DPS, 50% x 2, hardcapped by hit delay so there’s a limit to stacking attack speed, Double Punch only counting as 1 hit for auto attack buffs etc. The attack speed from Double Punch is said to affect all attack speed skills, but from testing, the amount is just too minuscule to even matter as “interaction” with other skills.
On the other hand, the rest of Monk’s skills can out-DPS simply spamming Double Punch in the update due to how low Double Punch damage is, but no one even uses it (ok, Hand Knife is buggy I get why no one tests that but the rest IDK).
The only thing good going for Double Punch is the fact that Monks can enhance Double Punch. I don’t know what IMC has in store for Monks, but for now Monks as a whole is flawed in general.