Well it probably means they wouldn't enter an assault out of it. Saying that load it up tot he nines with cheap stuff and attack the enemy bts after planetfall, you should wipe most BTS's out!
Since the Manta has eerily floated back into discussion (like the giant floating UFO it is) here is my suggestion for its stats.
Points are left off, as these are dependant on the resolution of the planetfall and support craft capability. However with the existing rules it seems to play at 6xx points (well I blew it up about as easily as I get Reavers

).
Manta - something or other config (to allow variation later on for sub lists), umm mech assault?
War Engine
Move 20cm
Save 5+ Reinforced Armour, Deflector shield (at a straight 5+), Damage Capacity 10
CC n/a
FF 5+
Twin-linked Heavy Railcannon, 90cm, MW2+, Titan Killer (D3), Fixed Forward Arc
4 x Seeker Missiles, 75cm, AT6+, Guided Missiles
3 x Twin-linked Ion Cannon, 60cm, AP3+/AT3+, Fixed Forward Arc
Multiple Long-barrelled Burst Cannons, 30cm, 4 x AP4+/AA6+
Support Craft - need to resolve rules
Planetfall
Markerlight
Fearless
Critical Hit Effect: Not sure. It was played as the deflector goes down but this leaves him pretty exposed and there is a 4/81 chance of any hit striking the Manta to do it. As you need (with the shield up) apr. 34 hits to kill it on average you will be losing it every game. Maybe instead have a crit that does D3 extra damage, or copy the FW manta crit?
Transport (may carry 38 infantry units, with battlesuits taking two slots each. Up to 12 light vehicles may be carried, taking two slots each. Up to 4 armoured vehicles may be carried taking 7 infantry spaces each, or 5 if they are Devilfish).
Transport is a bit complex but this is copied straight from FW. As this is x config could simplify it to 18 infantry stands and 4 vehicles or 6 light vehicles.
If thats not enough weapons you can add in the twin linked missile pod as well. But I think that is the Tau equivalent of a Reaver Titan class warengine (better short range, better all round, doesn't have the anti armour bias). The support craft/planetfall rules though will really determine its points cost and the transport ability is hard to quantify.
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