The concept of the Orb Craft is to change the combat paradigm. This isn't just through fluff text and rolling out some new guns and magic armor. The orb craft have no magic advantage in terms of arms or armor, and are limited capability. The area where they are going to break the balance of the game is through the use of rules and mechanics. Orb craft, given their size, their firepower, and their mobility, can do things that while some other vehicles can do, none can do them all.
1. Saturation Attack
Orbs can have a very large number of secondary weapons, dozens, even up into the hundreds. These are vehicle scale weapons, typically lasers, particle cannons, autocannons, gauss and coil guns, and missile batteries. The Saturation Attack doesn't target a foe, it targets a space, and everything and anything caught in that space is subjected to an absolute hellstorm of firepower.
Rules - An orb targets a specific 'hex' within it's medium or short range, and all non-capital weapons facing that hex are discharged. This massive attack cannot be dodged or evaded, only sheltered or endured. All units caught in the area designated for saturation attack are subjected to a random number of strikes from the secondary weaponry used. (I would use 1D6 or 1D6+1 hits as a general guideline). Larger objects are much more likely to be hit in this sort of attack. Infantry and power armor troopers might be able to luck their way out of it, but tanks, mecha, and anything else large is not going to get out without being hit at least once. Saturation attacks are typically used to flush out ambushes, attack dug in foes, attack large numbers of smaller foes and force them into defensive positions, and otherwise ruin a perfectly nice day.
Who can: Bombers, artillery fire support bases, aerial warships
2. Suppressing Fire
Similar to saturation attack, suppressing fire uses the secondary weapons to fire in a horizontal band across the area of attack. Anything that doesn't take cover or fall prone is going to be hit, a lot. The Orb craft can use it's capital weaponry in a suppressing fire attack for intimidation purposes, but anything smaller than a large mech is going to be under it's targeting threshold and is likely only going to be hit if they roll a critical failure on evasion or taking cover checks.
Like the saturation attack, the orb designates a firing arc and discharges any and all weapons it wants in that arc. Anything over 2-3 meters tall in the area is going to be hit by 2D6 random shots. For an orb packing lasers, few mechs are tough enough to laugh off being hit with 2-12 large laser strikes. The use of suppressing fire is best for facing mecha and other large vehicles.
Who can: infantry (vs infantry) mecha
3. Concentrated Fire
Should something pop up that is able to get through suppression fire and saturation fire, the Orb craft combat computer has the ability to focus all of the weapons on a single target, creating a virtual torrent of vehicle grade weapon's fire on a single point.
Also known as barrage fire, concentrated fire is intended to chew through cover, destroy fortifications, reduce even assault mecha to glowing slag, and wreck the ever-loving hell out of any small and medium aerial ships that approach the orb. The river of fire generated by the attack allows for the system to rapidly adjust and track it's targeting solutions. A foe can only evade concentrated fire so long before being caught by dozens of hits per round.
Who can: aerial warships
4. Indirect Fire
Owing to the fact that Orbs are equipped with capital grade weaponry, they are able to engage in artillery action, hitting targets behind cover by firing ballistic weapons in high arcs. They can use this to snipe enemy ships and heavy craft, provide support for other ground forces, and function as an artillery fire base that can fly.
Orb craft that use indirect fire have heavy autocannons or guided missiles and rockets, allowing them to make it rain in tremendous fashion. Beam weapons cannot fire in arcs, and most naval rail and coil guns have too much power to be used effectively as siege weaponry (being prone to lobbing their projectiles into low orbit). An orb can choose to rise to a higher altitude and use it's direct fire weapons as artillery, but this still requires a line of sight as their weaponry remains direct fire and not ballistic. Warships are capable of this as well, but orb craft are smaller and cheaper, and as such can cover more space than an equivalent warship.
Who can: artillery weapons, bombardment mecha, aerial warships
5. Alpha Strike
Most Orbs (an mecha, and warships, etc) fire their weapons in volleys and sequences, to regulate the use of ammo, energy expenditure, and heat generation. The Alpha strike option involves picking a single target and discharging all weapons at that target at the same time. Mecha will do this, and deal with overheating and being short on ammo after the fact, assuming that the alpha strike will defeat the target, or it is the only way the attacker can hope to damage said target.
After an alpha strike, an orb cannot move at above cruising speed, cannot rise in altitude, and cannot fire any of it's capital weaponry, and can only fire ballistic and missile secondary weapons in the next combat round. Warships generally cannot alpha strike as it is almost impossible for them to bring ALL of their weaponry to bear on a single target. Mecha can alpha strike, but dont have near the potential firepower. An alpha striking orb, that connects, can blow the guts out of a warship much larger than itself, and when an orb goes toe to toe with a warship, alpha striking will typically inflict enough damage for the orb to escape, or wound the ship enough that the orb and it's allies can move in for the kill.
Who can: mecha, combat vehicles
Fast moving aerospace craft are capable of strafing attacks, where everything in a certain line on the board is subject to a series of attacks from beam and rapid fire weapons. This isn't a precision attack so much as it is a disruptive one. If enemy ground units have started to assemble in a confined area, say massing for attack or preparing to offer a defense, the strafe allows the orb pilot to attack a large number of foes with the same weapon in the same attack phase. Secondary weaponry can chew up the ground, while the main guns, if energy based, can burn furrows through the ground and reduce armor and infantry to ashes and dust. Strafing works against large targets as well, such as making strafing runs against large ships and large structures. This generally requires the target to be several times larger than the attacker, but this is still viable against most capital ships cruiser and larger, and most space stations will also fit the bill.
Executing a strafe attack requires the attacker to be moving at at least cruise speed, and to designate a 5 hexes all in a single line on the combat map, and attack it with energy weapons or rapid fire weapons. Units in said hexes are subject to being hit by the weapons and must suitable dodge/evasion rolls. Missiles, low rate of fire weapons, non-lethal weapons, and such cannot be used for strafe attacks.
Who can: Aerospace fighters
7. Pandora's Box
The typical orb craft has several hundred tons of internal space/weight it can use on *whatever* and most of the time this is big gats, scads of ammo, and probably some more gats just for good measure. This space, however, can be repurposed for anything the orb craft designers want. While there is no shortage of arcanotech uber-weapons, and ridiculous gats, that isn't really worth noting. What is worth noting is that the typical orb has enough internal space to mount the same equipment as a spy/surveillance vehicle, or pods to drop special forces, or to carry a large amount of external cargo. Even with it's arms and ammo, an orb can be used as a heavy hauler to move pre-con tactical bases, STC facilities, or even any of the sundry list of superheavy vehicles like the Cataphract or TOG.
Most warships are not good for cargo moving, and there aren't land vehicles that can match the versatility of the orb craft. An orb craft can typically give up 10% of it's secondary armament and gain special equipment space for recon, electronic warfare, stealth capability, drone launchers, and so forth. An orb that drops one of it's capital weapons can pick up the hardware to be a mobile CogNet node, or be able to air drop battlemechs. One that removes its capital weaponry can become a mobile command center, a flying hospital, or even more terrifying for an enemy, a flying polyforge facility.