I don't know what you're talking about in regards to Precursors being immune to reality warping as that was never stated anywhere in Halo's lore. Constant and powerful gravity was enough to shatter Star Roads that we could guess were around a sun for ~10,000,000 years. If ridiculously intense gravity combined with complex orbits can shatter star roads, then I don't really see how they'd be immune to reality warping completely. You're also over-exaggerating the effects of Halo's pulse. A somewhat ambiguously canon factoid regarding Halo given to us by Greg Bear is that Halo's pulse can only kill life with the neural complexity of a squirrel or greater. All life below that is killed off by subsequent ecological collapse due to the massive extinction event and change in the food chain. By that point, the only life left would have the complexity comparable to lichens and moss.