Some of the studies were published after the trial (Chase and Shannon, for example), so I don't see how this is possible.
And it is not just one expert, is it? It is an unprecedented number of experts who are expressing concern about the safety of the conviction, the quality of the evidence used at the trial, the integrity of the prosecution's experts, and the quality of the initial police investigation.
If none of this bothers you, you either don't understand the issues being discussed or you are wilfully ignorant.
The police started from the point of Letby being guilty and worked backwards to prove it, allowing the consultants to act as assistant detectives; this goes against every protocol in place to minimise the risk of MOJs. Even if you do think Letby is guilty, that this happened and was allowed to stand should be concerning to you.
Evans also started from an assumption of guilt, is woefully underqualified for the case, and has a history of being a problematic expert witness. There is also evidence of witness shopping.
Much of the evidence presented at court is based on made-up science (air via the NG tube) that even the prosecution's witnesses no longer stand by, or untested theories (insulin in the TPN bags).
Regardless of Letby's innocence or guilt, failures of this scale should never go unchallenged.