AFAIK Dr Evans only looked at the medical evidence to identify suspicious/not suspicious events i.e. was deliberate harm done. I don't think he had anything to do with the shift charts. I think if he has anything to feel guilty about it would be overstating the certainty of his conclusions. Whether the system should be changed to make sure that experts are neither prosecution/defence but unbiased (and paid either way) is up for debate.
The consultants were responsible for selecting the cases to look at in the first place (some from going back over notes like the insulin cases, which weren't considered suspicious at the time, hence the definitive tests for artificial insulin not being done). If we're definitely looking for a murderer, shouldn't we be considering that a doctor could also be responsible and have independent people picking?
The police had access to the shift data so they (obviously) only selected events where LL was on duty. AFAIK the chart includes shifts where she was either on duty when the suspicious event/death occurred or the shift before.
The prosecution put together a narrative which shows LL harming babies. That's how the legal system works so they did their job in that respect. It's up to them to present the case that shows she's guilty and up to the defence to cast doubt on that.
The thing is, the more cases the consultants could pick out and the more suspicious events that could be identified, the worse it looks. Rather than taking each case on its merits - I mean, a single baby being murdered is a terrible thing, right? But it's difficult to prove. If you've got not one but 18 suspicious events and there's one person who was there (or thereabouts) for all of them, then even if there's no direct evidence of harm in any one case, then that's a lot of "smoke". Especially if you don't mention the fact that some of these events were not initially thought to be suspicious and other events have been dropped and you're not allowed to mention as defence any incidents that weren't part of the trial.
The judge allowed the jury to find guilt even if they were convinced that deliberate harm had been done and that LL was the person who had done it, but they didn't need to know exactly how it had been done. I don't think that's entirely fair in this case because the methods of harm put forward by the prosecution were so diverse (overfeeding with milk, insulin poisoning, air down NG tube, injected with air, "force of a car crash" injury to the liver etc.) so it's not like you can point to a single culprit with a particular MO or a particular "type" of victim. Normally in a murder case you'd start with a victim and try to find the murderer. What they ended up with here seems to suggest to me that they started with a murderer and tried to find as many victims as possible.