I believe Letby is probably a killer but technically "not guilty" because her conviction sounds unsafe. So the poll is too binary.
My credentials: I hold a first in Criminology (bachelors) and a doctoral degree in psychology, but to be clear not forensic psychology. I am not qualified to comment on the medical evidence but my lay opinion is that it sounds there may be enough reasonable doubt and therefore, by that burden of proof, Letby is "innocent". However, showing possible alternatives is not the same as Letby not being a killer.
Firstly, Barrister Mark McDonald obviously has ulterior motives. There are dozens/hundreds of unsafe convictions. Why has he got such a bee in his bonnet about Letby? My opinion is he is ego-centric and primary motivation is to make a name for himself. He has his eye on a gravy train of fame, television panels, and book deals. Very much a self-serving man in the pretence of rescuing an innocent person from a miscarriage of justice.
Something I can comment on with more certainty albeit still subjective is that the psychological evidence, from what I know of it, chills me to my bones. Admittedly it is circumstantial and certainly not enough to convict someone.
Thinking of Letby from an "object relations theory" and an understanding of "narcissistic supply". I believe Letby's motive was the playing God theory, or perhaps a sort of munchausens by proxy.
I understand Letby grew up being told she is a miracle baby saved by a nurse. If this is true, it is not coincidence she decided to become a neonatal nurse. These types of events do become a key driver in someone's life, I have seen it many times. Moreover, like most serial killers, you don't go from nothing to serial killing. So if this fact about her birth is true, in my opinion Letby started practicing "saving babies" and this became a big part of her fantasy/phantasy life.
The babies are like objects in her ego and sense of self. Everything about them, the parents, the nurses and doctors, the drama, this is feeding Letby in a narcissistic way. Fuel for her ego. This for me is the explanation for her obsessional searching for families on facebook (both survivors and the deceased), and why during the trial it was reported she showed a numb affect when speaking about the deaths but then emotional lability when she referred to how she was affected.
Again, my information on this is all second hand and there may be more detail on the psychological aspects I am missing. But just from the face value and having worked with a number of offenders that deny their crimes, I am confident to say she is probably a killer.