What is 30 RP to DW Frost? It is 2.05 FS's and 0.92 HB's.
What is 30 RP to 2H Frost? It is also 2.05 FS's, but 0.46 OB's and 0.21 HB's.
What is 30 RP to Unholy? It is 1.07 DC's, 0.43 SS's, and a variable amount of DT uptime depending on DC frequency.
The damage of these is not remotely comparable.
Unholy also barely generates enough RP on average to use this SR on CD with a 30 RP cost, whereas Frost has no problem with this availability.