The near-C rock discussion is almost easier to swallow: a technology appeared on the scene that changes the rules of the universe. There's a different problem with planetary systems that have been supposedly around for at least hundreds of millions of years that would destabilize almost immediately and that is regrettably built into the system generation rules. To an extent Traveller brought this on itself, in Book 6 it lists equations that can be derived from Newtonian gravitation thus implies that the universe operates by those rules and invites players to exercise those rules but collapses when some of the examples are tested at more than a surface level. Like a sore tooth that you can't help but push at, it's kind of hard to leave it alone. In part because it feels like it could be fixed.
That's a diversion from the point of stellar scale engineering structures being cool and fun, but I think I had it in my mind probably from 8th grade to when I had a class that touched on perturbation analysis that Klemperer Rosettes were stable because I presumed Niven inserted them into the Ringworld universe for that reason. Cool as Niven and Traveller are, make sure you don't base any part of your perception of reality on them.