To be fair, you can't prove the bolded part of this sentence. That is why the State agreed to the Alford plea also. The State would have had a huge upward battle, 20 years after the fact.
But I can agree with the first part of the sentence: that the WM3 were convicted based on all of the evidence that was presented -- not just the "satanic cult" angle -- but all of the evidence. The injustice was, that the original jury took into account the JM confession. That rightfully should have never been allowed in deliberation, and arguably, didn't even need to be introduced. Honestly, if that never was, I don't think the WM3 would have ever gotten out of prison -- and it was not only unethical but utterly stupid for the foreman to introduce that. If the jury needed that to convict (which I don't necessarily believe they did, but I digress), then they should have never found DE and/or JB guilty.
No, I cannot prove that. The point is, by accepting the Alford Plea, the WM3: "admitted that the evidence the prosecution has would be likely to persuade a judge or jury to find the defendant guilty beyond a reasonable doubt".
Good points on the rest of your post. I agree that even without JM's confessions, they would've been convicted. The culmination of all the other evidence (nons denying its existence doesn't make it go away) was incredibly damning. However the JM confessions were incredibly powerful as well, even if they shouldn't have been allowed into the courtroom.