Maybe it’s a semantic issue, but I find it difficult to call either Regensburg or Schweinfurt “precision” raids. From Malthus’ cites, the former involved 146 bombers, of which “126 dropped 298.75 tons of bombs”. A total of “60 bombers lost and many more damaged beyond economical repair”, but this is irrelevant to the point. Similarly, the Schweinfurt raid involved 230 bombers, of which “183 bombers dropped 424.3 tons of bombs”. Losses were equivalently catastrophic, but again that’s not the point.
It seems to me that calling either of these “precision” raids was more propaganda than reality, with the only rationalization being that the targets were factories rather than entire cities. One might expect that more than 700 tons of high explosives, delivered in a “precise” manner to discrete and well defined factory installations (not hardened targets, but common buildings and shops), would be expected to pretty much remove them from existence. But while Regensburg received “heavy damage”, “the Schweinfurt raid had been a failure. The excellent results at Regensburg were small consolation for the loss of 60 B-17s. The results of the bombing were exaggerated, and the high losses were well disguised in after-mission reports.” And even there, much of the damage was caused by secondary fires ignited by incendiaries. Such would have no parallel if the targets were railway bridges, let alone selected structures in a death camp.
As for the Dambusters, these were indeed highly precise but highly specialized attacks that involved unique equipment and intensive training. And for all that, only 2 out of the 3 dams targeted were actually destroyed. Again, there is no parallel between skipping bombs and an attack on railways or crematoria.
I can admit the possibility that a small, well trained strike force might be able to inflict heavy damage on a single selected target, like a bridge. It might take several tries, but given the will, and acceptance of whatever losses might be sustained, the result could be achieved. And if that bridge led to, say, Buchenwald, then that camp itself would surely see a curtailment of incoming prisoners for as long as the bridge remained unrepaired. But given the nature of railroads, I don’t see that it would be impossible or even extraordinarily difficult to redirect those prisoners bound for Buchenwald to any of the other hundreds of available camps. Nor do I see any reason to believe that Buchenwald itself would need to reduce its extermination schedule for prisoners already within its walls. Likely the bridge would be repaired long before they ran out of on-hand people to kill.
At any rate, none of these examples convinces me that the Allies had any great facility for precision air strikes of the kind or the repeatability necessary to significantly interrupt the Nazi death machine.