Aren't the Clans resource poor?
The Clans don’t appear to be poor in fusion engines. Even their lightest combat vehicle, the lowly Shamash, built by the poorest Clan, the Blood Spirits, employs a 60-rated fusion engine.
That seems like a lot of resources.
It depends on where the economy of scale lies.
If you already have lots of production lines for various small fusion engines — as the Clans appear to— it’s almost certainly cheaper to just churn out more copies of those small power plants for stationary use rather than build a big, one-off power plant and all the associated power distribution infrastructure.
If you have no existing small fusion engine production lines, then it may be cheaper to build one, very large fusion powerplant and all the associated power transmission equipment rather than create a production line for smaller fusion engines from scratch. But that’s not the situation with the Clans.
Yes Scientists survived but we also know that the rebuilding was hampered by the loss of so many scientists. That means they lost a lot of knowledge and that the survivors had to learn more.
Maybe. Like with the power infrastructure, there should be a lot of independent duplication across the Clans when it comes to technical knowledge. Anytime one Clan makes an advancement (new phenotype, weapon, design, etc.) that knowledge quickly spreads to the other Clans through trials, trade, or isorla. The only knowledge that could be permanently lost is knowledge possessed by only one or a few Clans, and there doesn’t appear to be much of that kind of knowledge at all. Yes, the Blood Spirits, Fire Mandrills, and Steel Vipers lost the knowledge to produce ER Pulse Lasers because they went extinct. But the Cloud Cobras, Coyotes, and Star Adders didn’t. That knowledge still resides with those Clans.
This discussion really comes down to what degree Society machinations and Warrior Caste inattention was holding back Scientist Caste progress prior to the Wars of Reaving. To a degree, it doesn’t matter how many smart, knowledgeable experts you have at your disposal if the bulk of their work is being diverted by a cabal (like the Society) or ignored by their customers/leadership (Warrior Caste).
The Wars of Reaving certainly shrank the the Scientist Caste in the Homeworlds and may have resulted in the loss of certain, limited knowledge bases that the surviving four Clans never had access to. But it may not matter after the Wars of Reaving because the research output of the remaining Scientist Caste is now being fully directed towards and utilized by those four surviving Clans. Who knows what technical knowledge the Homeworlds Clans are capable of recovering or advancing with the Warrior Caste finally paying attention and no secret cabal keeping the best research for itself.