lets say it like this
IMO for the single usage mechanic the tooltip should be like this:
“after using wake of washes, wake of ashes is replaced by holy hammer for one usage within 12 seconds” or something similar that makes clear that it is a single usage in a 12 seconds window.
but because this specification of “one single usage” is missing in the original tooltip. It describes a multi usage scenario because the skill doesn’t have a cooldown.
(adding a cooldown to the skill would be the alternative way of restricting it to less usages)
But there is no reason to interpret the original tooltip in a way to be a single use mechanic - because we never saw consumers with single use mechanic before.