I think a bit part of this perception about the "brutality" and "test match intensity" of the NZ derbies comes from the relative positivity of their TV commentators and press vs the Aussie moaners. The Kiwis are always talking up their own players and teams but the reality is they miss tackles and drop balls too. Their commentary just doesn't seem to focus on the negatives as much as ours.
If you set aside the Waratahs' games (because they were truly shithouse) from the pre-covid games the rest were pretty even:
Brumbies 22 vs Highlanders 23
Chiefs 14 vs Brumbies 26
Highlanders 22 vs Rebels 28
Crusaders 24 vs Reds 20
NZ 83 vs Aus 96 (add the Tahs games in and it's 147 - 209, the other way)
Against Saffa teams it was 4 Kiwi wins vs 3 SA.
It's a small sample but do the NZ teams only bring out the brutality and test match intensity when they're playing each other, or is it just marketing and spin?