Nostalrius Begins - Quality wow vanilla realm (1.12)

Was looking on Youtube at random Nos videos and found this:
https://www.youtube.com/watch?v=HzoWUULv_ag

Bonus frost spell damage seem to have very little impact on its damage.

Did anyone els tests this?

Instant and channeling spells receive less actuall DMG from +DMG on gear then
a castable spell like frostbolt. And yes thats exactly how it was in retail.
Its a differen equation , not really sure how it works precisely , all I know is that the cast time
on your spells in taken into account.

Blizzard Spell http://db.vanillagaming.org/?spell=10187
Is marked as both ChanneledInstant for Vanilla.

But ok thanks for clearing that up.