Just two points in response to the above selections from your remarks, since I think we've rather covered the other matters in subsequent posts. (If you disagree, I can try to circle back.)
First, notice what you say about George dM: a huge amount of WC testimony, much more, in fact, than would ever have been allowed in an adversarial trial, where much testimony would have been objected to and probably excluded, and the judge would not have allowed the questioning to go on and on. So, with George dM we didn't have adversarial procedures but we did get a much more relaxed, open-ended kind of fact-finding, though still sworn, that allowed for digression and development. Which approach would yield more information, on balance? I don't feel the public would necessarily have been satisfied with George dM's adversarially "sculpted" testimony--which would necessarily have resulted from regular trial procedure. Wouldn't later critics typically complain, "The judge cut him off just when he was going to give us the truth?" and so on.
Now, as to a civil proceeding, which you suggest as another possible model, recall that at the start of a civil action in the United States, there is extremely wide-ranging, nearly unlimited "discovery" by the parties: capacious requests for documents; interrogatories; requests for admission. And then the live depositions start. Depositions can take hours or days, sometimes weeks in big cases; while attorneys for both sides are present at depositions, they are supposed to be largely passive. There are virtually no evidentially limitations, except for objections to the form of the question (compound and such) and to privileged matters: no objections to hearsay, irrelevancy, prejudice, and so forth.
When all that massive amount of evidence is gathered, and unless the case settles (as it usually does), we go to trial, where we are now in full-on adversariality, and all that previous discovery material gets "sculpted" in the trial process.
Actually, civil litigation is a good tool for thinking about the WC as opposed to adversariality. The civil discovery process is very like the WC: wide-ranging fact-finding, a desire for more material rather than less--sworn and subject to lawyers' ethical rules, of course--but not subject to taut trial procedures. The eventual civil trial, if it happens, is more like what you're advocating: many evidentiary exclusions, a much more trial-shaped truth.
Given that LHO was beyond earthly suffering, I feel the American public was better served by the WC's more-rather-than-less approach as opposed to adversariality's less-rather-than-more.