It could at least have been explored. I wonder if putting Jeremy on the stand was also in his best interests?
1) The COA nailed on the head why the defense didn't discuss the Bible. The defense was quite happy that the prosecution didn't bring up the fact that the Bible was placed in Sheila's wet blood after her death. This fact supports the conclusion someone else was there at the scene after she died before her blood dried. It thus provides support for the blood evidence that someone was there staging things. If the defense brought up the Bible in order to refute their claims the prosecution would discuss this and it would be another problem to deal with instead of a help. When the other side gives you a gift by missing an argument you don't help them out by providing them with a reason to change course and use it.
2) Unless someone posts Jeremy's full testimony we don't have a way to evaluate if it was more helpful or more hurtful. Part of his testimony I saw was not helpful in my estimation. He testified that at first he didn't appreciate the significance of Nevill's words. He said this is why he didn't think about calling 999 plus he didn't think it would be faster. After he fully woke up and thought about it then a sense of urgency struck him and he decided to call police. his doesn't really help explain away his failure to call 999 and conflicts with his claim to police he immediately phoned police. Furthermore, he maintained he called Julie after police though the prosecution did a good job of establishing he called Julie first. His story is not a good one given he called Julie first. Calling Julie though he didn't appreciate anything significant makes no sense. I would have whante dhim to have a better story than this to tell if I was going to allow him to testify. Of course the decision is ultimately up to the client but we can pester the hell out of them to tell them not to if we think they are not going to do well.
We don't know just how bad he came off in the entirety without seeing the full transcript. the prosecution lost his transcript and the defense didn't provide it to the appeal court so the defense must have decided not to keep it. That seems odd unless he did poorly but even then you would want it to be able to see how poorly he did and try to find a way to mitigate it. The government only has his cross examination. Both sides losing his testimony transcript is just one more odd thing.