The tech degradation of the Succession Wars was probably due, in large part, to the massive losses of infrastructure and trade routes.
Let's say you've got a factory that is churning out Lancelot battlemechs. Then the First Succession War hits. Even if your factory doesn't get bombed, you still might not be able to continue producing your mechs. What if the Happy Freight Shipping Company (who has always delivered your orders of XL Engines from some distant planet) has their jumpfleet wiped out? You try to get another company to deliver, but things are tough all over, and maybe there's just not enough shipping capacity now.
Or what if the planet you're on doesn't get hit, but it does require specialized parts to keep its water purification system operational. Some far away world gets nuked, and they were the ones that made those specialized parts. Now it's only a matter of time before your planet can't support its population. Now that might take 50 years before the lack of parts becomes a big problem, but it's coming.
The First and Second Succession Wars blasted apart a bunch of highly interconnected economies, and things continued to fall apart during the long Third SW. It doesn't mean that people were getting dumber or forgetting how to make things, or that they lost the ability to invent stuff. It just means that by the 3rd SW, everything was falling apart. It would be no big surprise if you had to shut down your factory because that last jumpship finally breathed its last, and the factory that makes new jumpships can't be restarted because there's a missing piece that isn't made anymore.
The speed of the tech recovery after finding the Helm Memory Core seems to suggest that a lot of Inner Sphere factories weren't annihilated, they were just dormant. I don't think that was the intention during the early days of Battletech, but post-Clan Invasion when FASA needed the IS to jump-start production, it became that. Now many factories were just waiting on a few key replacement parts. Once they found the HMC, people on various planets would have had the info on how to make those replacement parts that they had long needed, and then it was only about 20 years before they were climbing back to pre-SW levels of technology and production.
If that's the case, then ComStar's assassinations could be seen more like a desperate attempt to prevent an inevitable tech revival, rather than them systematically kicking the Inner Sphere down the tech tree. ComStar had been playing whack-a-mole trying to stop people from rediscovering everything, but the HMC meant that it started happening too fast for them to keep up.
So no, I don't think it's unreasonable to have someone figure out a problem that the Star League had been chewing on. It sounds like you only need someone to find a Star League research facility who were this close to discovering a new thing, and then they figure out whatever the last step is. Shouldn't be too hard to believe.
