On April 18, 2005 Halo 2 received the Auto-Update 2 (1.1a) which updated/changed various aspects of the game including melee damage.
> Melee Damage: Melee damage has been increased across the board as a counter measure of sorts to close-up dual wielding. Jumping strikes are now much more powerful, often resulting in instant kills, while the general potency has been increased for normal melee attacks and the Brute Shot has been given a specific melee attack boost, in recognition of the fact that it has a huge scythe attached to it. This actually makes the Brute Shot a go-to weapon in a lot of new situations.
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> Examples of the increase in power include one-hit kills from many jumping strikes, two-hit kills from the Brute Shot melee attack, and far more power on torso and head strikes from all other weapons.
Can anyone confirm if this update to melee damage was applied to the campaign as well? I can confirm this is accurate for Halo 2’s multiplayer in MCC (as the Halo 2 we play is technically Halo 2 Vista which released on May 22, 2007.)
Another piece of Auto-Update 2 fixed Sword Flying in matchmaking, but it was left in campaign deliberately by Bungie. This makes me wonder if there is no parity between Matchmaking and Campaign updates, as this would be consistent with future title’s updates such as the Halo: Reach Title Update (brought to us by our very own 343i!)
Here is some hard data on Halo 2 melee damage values pre and post Auto-Update 2. Somehow it is the only text I can find online, but it does align with my previous and current knowledge and experience playing Halo 2 before and after the update.