This forum is not a court of law, nor even a platform for formal debate. No ivory tower, this.
This case is a slam dunk. A good defense team would advise Oswald to plead out.
And what some call 'discrepancies', others might call minutia.
It appears that the Oswald defenders think the WC shouldn't have conducted an investigation because they may have found someone culpable in the assassination. In this case Oswald. And that would have violated his (or others') non-existent, for the WC investigation, right to a presumption of innocence.
The presumption of innocence is, as you point out, for a court of law. It's for a criminal proceeding and for the jury to adhere to. The WC wasn't a criminal proceeding. It had no power to indict anyone; even for perjury.
So the Warren Commission was wrong because they accused Oswald of a crime. And that was a violation of what? His right to a presumption of innocence? But he was dead and he couldn't be prosecuted. So we can't have an investigation - that would violate his rights - and he couldn't be prosecuted - he was dead. What was supposed to happen?
This is why we call them Oswald cultists.
And just to note: Jim Garrison accused all sorts of people, including dead ones (Ferrie), of crimes. Murder, conspiracy to murder, perjury....and some (not all but some) of the same people upset at what happened to Oswald are largely silent. In fact, some are big Garrison defenders.