Totally agree! Frankly even in the deep periphery, one is bound to get 1 genius per generation who actually pushes tech forward. Furthermore, if there is something very interesting about the deep periphery is that many of its planets are quite 'heavily' populated (say with a population akin to Brazil or so). So even if the educational system was lacking in coverage, there still would be some advancement over time - to make a historical example - akin to the renaissance in Italy. Additionally the deep periphery is not normally troubled by constant warfare or planet killing pirate raids, and therefore more prone to prosper over time.
Do you have ISP3? It provides several examples of how technology can stagnate or be lost.
War - Just because they don't suffer from the Succession Wars doesn't mean periphery planets don't have that limit their technological development or causes them to lose technologies. Example - Alexandrian Covenant (early). War, or the threat thereof, has also frequently been a driving force behind technological development including computers, communications technologies, rockets, medicine and airplanes.
Culture/Religion - Societies occasionally develop where technological innovation is not a pressing concern. Examples - Union of Samoyedic Colonies, Society of St. Andreas, Dante and Alexandrian Covenant (late). Detroit, possibly the most advanced world in the Periphery, was founded
Environmental - Environmental issues can limit technological development or drive it in a specific direction. Examples - New Delphi Compact, Frobisher and Midden.
Lack of specialists or a basic understanding of underlying technologies - One can't develop more advanced technologies without a basic understanding of the underlying technologies that make it possible aka you can't go from horse drawn carriages to JumpShips without developing at least some of the technologies that lie in between. Example - Axumites
Other factors:
Motivation - The desire or need to travel into space has to outweigh the cost of developing the technology for the effort to be made to develop it. We have known for decades that we live in a world of limited resources but we have several curtailed our efforts to seek new sources off-world.
Matter of timing - Sometimes geniuses are born before their time aka before their theories can be made possible whether due to technological limitations or the astronomical cost of development. Examples - Michaelangelo, Professor Kearny and Professor Fujita.
Lack of raw/vital materials - Lack of vital raw materials can easily limit technological development. Only a small percentage of worlds have ready supplies of Germanium without which JumpShip construction is impossible. Even if Germanium is available in the system, the locals may lack the ability (or technology) to find it or mine it. Examples -
Actually, the idea that shipyards are difficult to come by is also rather silly. When the Clans came knocking, everyone and his brother built additional slips to engage in a massive shipbuilding spree. And if germanium is the bottleneck, please note that some of the best sources of the material actually lie in the periphery (the Marians and that pirate mine/shipyard which I forgot its name).
Even the Inner Sphere powers, with the exception of Necromo shipyards, didn't build entire shipyards from scratch, they expanded existing ones if they didn't simple reassign existing slips to WarShip production.