Do not forget the "Lance" story.
It came to mirror the same name rule for 40 3rd Ed Eldars.
At this time, the rule counted any vahicle armour better than 12 as 12. the Falcon lance weapon was S8, so it needed never worst than a 4+ to pierce the armour.
The lore justification was the eldar tech is so advanced they didn't create weaponry that could be effiscient against their own forces. And indeed, no eldar vehicle had a better armour than 12 (even the super heavies).

So, the goal here is to level enemy armour to be average and no reduce everything. The difficulty of choosing the right target to benefit from it is very eldar-haughty, so lore friendly ^^
And, I think it has been smartly converted to Epic.

It is still a good rule but still a weird one.

No need to say there is no current counterpart since that rule disappeared with the 8th-9th Ed ruleset.

Didn't you notice we are talking about Tau here??? nobody mentioned Eldar but you

Not really, the thread is about changing the Lance rule, in the Rules Amendments subforum. If this were done it'd apply to all units, including the Fire Prism which was the where the rule came from in the official rules (Lance was published in Swordwind, not the main rulebook). Hence it's valid to consider the original intent behind the rule, even ignoring the balance issues with changing a core rule across several units.

That said, I think we reached a fairly watertight conclusion with the topic:
1. Leave Lance alone
2. Create a new rule e.g. Armour Piercing
3. If ACs want to give it to the Hammerhead and not the Fire Prism, cool.

Nope, the thread is not about changing the Lance rule. It is about replacing it with ArmourBane in the Tau lists (pretty clear just by reading the title of the thread...).