I never said that Silence was to be used on Eventide.
The only moment you can use Silence on a DRK is when they plunge in, else they're just at the back of their team waiting for the engagement to start. If they're behind or within their team, being silenced is meaningless because they're safe, and can safely ignore it (why would they waste purify there?). When they do rush in, they'll have purify up, making your silence irrelevant.
I do not know how to explain it better.