By reading this.
In regards to the “mysterious” Cadence cooldown, it is a very straightforward mechanic implemented to avoid issues with WPS skills that hit multiple times. I vaguely recall that there may also have been issues with passthrough projectiles on ranged weapons and Cadence, but it’s been I somewhere around 4-5 years when this mechanic was introduced…
In any case, the internal cooldown is a fraction of a second to prevent multiple charges of Cadence to build.
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You may occasionally run into this cooldown at extremely high attack speeds, but it’s going to have little to no impact over time.