Even the non jump capable Orky is somewhat overpowered because:

• It is very tough up to being invulnerable in the early game. They only thing that does actually counter it is mass bombers.
• It can be built very quickly.... from a harmless colonly ship that is not even easy to miss but cheap to replace.
• It weapons upgrade are very quickly built, allowing it to kill anything effortlessly what somebody can field at this stage of the game. They are also very devastating, quite capable of forcing a level 3 or 4 Titan into retreat.
• Its durability is very high and can quickly be upgraded to withstand anything but late game bomber spam.
• It is mobile, which make all the above arround 3 times as deadly... because you can never avoid an Orky.
• It carries phase missiles. Since Phase Missiles are the first thing to research with Vasari even in early stages of the game Advent cannot even hope to deal with it with Titan or capships. The increased damage does the rest, even for TEC. 

The developers probably wanted the Orky to be both an early defense weapon - which is ok and a late game offensive weapon - which would still be halfway acceptable, assuming it is really in late game.The problem is, balancing wise it cannot be both.

In reality the Orkulus is a excellent early defense weapon, probably the best defense one can wish in early to medium game

but even more so it is an nearly unstoppable offensive weapon.

1 single colony ship that slips trough..... and you can say goodbye to any of your planets, including but not limited to your capital. There is nothing you can do to stop an Orky until late game has been reached. Early game Orkulus rushing is a very cheap tactic that requires neither skill nor are the costs very high in case of failure.

The Orkulus was intended as a defense for the weaker Vasari early game. This is the reason it is at tech 2. Unfortunatly this also means you can Orky rush your enemies very early...... and there is no corvette fleet that can deal with an Orky under construction. Even if you enemy had managed tech 3 or 4.... he still has very little against the building menace at his planet. Ogrows are still far away and far more expensive than an early eco can handle to field them in high enough numbers. Adjucators are terrible in lower numbers and you can field even fewer of them. Not to mention both Ogrows and Adjucators are worthless against the enemy fleet.

Vasari fleet + one building Orky = certain loss of planet. Permanently too, until you can field 100 bomber wings or so. If you make a stand before you will loose planet +  fleet + capships + Titan.

I realize the Orkulus was meant as an Anti Structure cruiser..... but leaving the way to easy rush aside it is not used in this capacity. Instead it used an an offensive support weapon that rivals a high level Titan in terms of firepower and durability without having its flaws. 

As an early game rush anti structure starbase it is imbalanced. And in late game Vasari dont use it for that purpose anymore because they have their phase missile bombers.... which also need to be nerfed but that is another topic.

So the loss of the functionality would not hinder the Vasari much. So move Assault specification to Tier 8 and leave it there.

The Orkulus second intended function was to allow early game Vasari defense. This is mostly fine although even there its mobility imho justifies a longer build time and more important - a far longer upgrade time.

I often have the following situation in my games:

Vasari fleet is in full retreat, their low level Titan heavily damaged. They run.... my fleet in hot pursuit. Pursuit last for 3 systems and I manage to do a bit more damage to their ships. But in the fourth system he just build a fresh Orky.... and a repair platform any my considerable superior fleet doesnt stand a change anymore.

You say this is true for all starbases? Thats right, but

• other starbases are build my a expensive slow constructor and cannot move. This forces your enemy to place it for the future. And so the base constructor has a longer journey ahead of it. The Orkulus however can be build right the moment you jump in.... and will be a deadly threat to the entire gravity well afterwards. 
• I can avoid other starbases... you cannot avoid an orky. For example I can attack other buildings and leave him the choice to engage and risk his fleet or to let me do some damage... with Orky.... his fleet can sit idly repairing while the Orky makes sure I leave the gravity well soon or stay permanently by dying.
• Its movement ability allows the Orky to join with its fleet at will anywhere it pleases in the gravity well.
• You dont manage to get repair bays up close to the enemy fleet... build them farer away and then move your fleet and starbase right there.

So balancing of the Orkulus should resolve arround those 2 goals:

• Early game defense but little offensive capability
• Late game powerful starbase

To achieve this goal I propose the following changes to it:

1. Build time: You already have the advantage that your constructor doesnt need to be at the target location, so a 30 % increase in build time should not hurt its intended purposes. 
2. Speed: The Orkulus is to fast. It can cross even large gravity wells in under 1 minute, making any evasive attempts more or less useless - unless you bomber spam. The initial justification for movement was anti structure cruiser replacement. Well. structures dont move.... so half its speed and the Vasari for a change has to put some thought into it.
3. Weapon Upgrade time when owned gravity well: Unchanged - defensive is ok - with the speed reduction from above.
4. Weapon Upgrade time when in enemy gravity well: +400 % 
5. Armor upgrades = the same
6. Being a mobile starbase the Orky is invulnerable to many abilities designed to counter large ships. So either make more abilities affect it or reduce its speed down by 90 %, so that I can actually use my superior ranged units. 
7. Reduce the ammount of ressources gained by scuttling it. 
8. Perhaps its armor while being built should be reduced, too.