The Death Coil is set up as a toggle.
I can enable/disable it.
When it is enabled, there is an equal chance of HB, FS, PS, or DC.
When it is disabled, there is an equal chance of HB, FS, or PS.

Frost Strike is higher dps, when things are in melee range.
So that is when the Death Coil is disabled.
98% of my play was battlegrounds, and most of the time people were both ranged and melee.
It's better to use Death Coil, then to have Runic Power and not use it.
So DC was/is enabled most of the time, but not always.