But you just said one of your nobles builds/captures them on the border with the extents and ships them "south" (mapwise) to the Sol frontier... or did I misunderstand?
Not sure how you got that idea. I used the Solomani border as a bit of colour and an example of where corsairing happens. I pointed out a standard design is by nature Imperium wide, the ships can be built anywhere. I also offered some reasons why Vargr have similar styled ships (ie: they begged. bought or borrowed the plans and tech from a local Imperial shipyard then copied and adapted them.)
In my view Corsairs will be fairly common, especially in the peace that follows a war. Merchant routes need extra escorts in these times when the Imperial Navy is still licking its wounds and regrouping. There could easily be five to ten years of relative lawlessness in the star lanes before authorities get back thier hold.
Opposition for escorting Corsairs will include;
- Deserters with Patrol Cruisers, Close Escorts, Scouts and armed Merchants. Fighting for food, loot and spare parts.
- Enemy elements up to Destroyer size fighting their way back home after extensive battle repairs on some Imperial backwater.
- Profiteers, looking to capitilize on the relative chaos, robbing Merchants of thier ships boats (worth millions each)
- PTSD victims gone over the top, creating havoc because they can. Supported by a third party (Noble, system, Megacorp, etc)
- MegaCorps, looking to gain commercial advantage in a particular system or cluster
- Systems wavering in loyaty to the Imperium, intercepting merchant traffic passing through thier system.
- Devastated planetary populations needing to capture jump capable craft. Can think of many reasons for this.
- Belters without a trade (no more Ore ships coming) wanting to earn credits.
- Other Corsairs looking for a fast credit...
So where is the Fleet? It'll be refitting and repairing as fast as possible in order to be ready for the next conflict. Those assetts that are operational will be either patrolling the borders (all borders not just the recent conflict, in case other empires have a go whilst the 3I is refitting) or held at Naval bases ready to defend the Imperium and buy time for the fleet to build back up to full strength.