I would agree that Manticore had a silver spoon inserted, somewhere.
One factor that protected Manticore was logistics. Weber only alludes to the issue of fuel consumption and supply, but we are left with the impression that Honorverse starships are not analogous to nuclear powered wet navy ships out even sailing ships. Their endurance and range is not unlimited. The Warasawki sail enhances endurance and range, but that was not always a safe mode of transportation.
As of the time of the wars with Haven, warships were comparable to oil fueled wet navy warships. In prior centuries, they were more analogous to coal fired warships. No Navy in their right mind would deploy a significant fraction of their fleet so far from home that they could not reach their destination and return home without refueling unless they had secured refueling bases along the route. These bases in turn needed to be defended. As a result, only a fraction of a Navy's ships could be deployed at great distances. You see the legacy of this strategic thinking in SVW.
I recall a certain genius who once posted on this forum utilizing the information provided by Weber regarding Honor's use of fusion thrusters to sneak up on the Havenites who apparently had their headers inserted to deeply to notice fusion exhausts that were brighter than planets. If IIRC, the estimated fuel fraction was about 20%. The fuel fraction and thus range can easily be increased for freighters, but fuel is bulky. The need to about a warship imposes a limitation on fuel fraction and thus effective range.
The bottom line is that up until about 1800, Manticore was protected by distance. No one who could conquer them would try to conquer them until the existence of the Manticore wormhole junction was deduced. Even then the conquerors were a bunch of mercenaries who probably over extended themselves.