Comparing the Hammerhead with two other Skimmer TanksThere are always pitfalls in comparing things from army to army since it is rare for two armies to have an identical unit, so I thought I'd get a disclaimer out of the way first so that reader's know I am aware of this:
Disclaimer: The Following Comparisons are FlawedWith that out of the way I will compare the tank-killing ability of the Hammerhead with two other vehicles that are from Xeno armies, cost exactly the same amount of points, have moderate armour (5+ vs 4+), are Skimmers, move fast (35cm vs 30cm) and have ranged AT weapons.
The main flaw is range, while the first 3 tanks compared all had a 75cm primary weapon, the two below have 45cm which is obviously very significant (although see "The funny thing about Range" below).
The other is that neither of them are really tank-hunters and both have other obvious purposes. The problem with the railgun Hammerhead is that it doesn't take a tank-hunter to beat it at hunting tanks.
Reposting the Hammerhead stats for your convenience:
Eldar FalconThe Falcon is a transport; it has a dual role in delivering troops and supporting them in Firefights (FF4+), and also adding some AT/AP shooting.
Despite that, I will demonstrate that it is remarkably competitive with the Hammerhead in an AT role.

The falcon primary weapon is
twice as good at killing targets with 4+, 5+ and 4+ Reinforced Armour. It is twice as good as the Hammerhead whether sustaining, moving and shooting or doubling and shooting.
The reason for the improved results is that the Falcon Pulse Laser fires 2 shots (2x AT4+) at the same power as the HammerHead's Railgun. Caveat: the range is 45cm, other tanks compared here have a 75cm primary weapon
If the Hammerhead fires on a target with Markerlight support and a seeker missile, it is still considerably less likely to kill the target than a Falcon (eg 2 Hammerheads + Markerlights required to kill 1 Predator, only 1.5 Falcons required to kill 1 predator etc)
Shorter range (45cm), faster (35cm), can transport units.
The funny thing about RangeDid you know that if a Falcon moves, shoots and moves it can hit a target 80cm away from its start and end position and still has a higher chance to kill it than a Hammerhead that Sustains fire on a target 75cm away from its start location?
Eldar FirestormThe Firestorm is an anti-air craft weapon - one of the game's best with 2x AA4+ shots at 45cm range. Its secondary role is to deliver troops and support them in Firefights (FF4+), and its tertiary role is AT/AP shooting.
Despite that, I will demonstrate that it is remarkably competitive with the Hammerhead in an AT role.

The Eldar Firestorm is better at killing targets with 4+, 5+ and 4+ Reinforced Armour than the Hammerhead is, whether sustaining, moving or doubling and shooting.
The Hammerhead is better at killing targets if they are markerlit, but not by a huge margin. In fact Eldar Firestorms that Sustain are as likely to kill their targets as Hammerheads with Markerlights without Sustain.
So as mentioned, the difference in range is significant, but I hope that these comparisons show just how underpowered the Railgun is compared to some of its peers.
GW's description:
The Hammerhead Gunship is the main battle tank of the Tau, and all enemies who have encountered it quickly grow to respect, if not outright fear, the might of its main armament - the dreaded railgun.
There are many accounts of single Hammerheads demolishing enemy armour with almost contemptuous ease.
During the Damocles Crusade, the Hammerhead gained a particularly fearsome reputation amongst the Imperial Guard. Entire armoured companies were destroyed before they could close with the Tau battle lines, and whole offensives were transformed into fields of wreckage by the formidable Hammerhead gunship.And it has a profile to match: Strength 10 (out of a maximum of 10) and Armor Penetration of 1 (the best in the game).
In Epic the railgun is half as powerful as the pulse laser on a Falcon transport, and about as powerful as a Firestorm's Anti-aircraft gun (as long as the Tau player is risking markerlight on the target).
I could get my Vior'la Tau list rushed through the approval process much quicker if I didn't attempt to address this but would rather see if this ongoing issue can't be fixed once and for all.
Coming soon - suggestions for changes, what their affect might be, and cost implications and pricing ideas.