There was an interesting comment on the Reality Bomb podcast to the effect that all the interesting parts of the Tecteun story have already happened and all we get is the Doctor feeling sad about it which is inherently undramatic. I thought that was very insightful - and interestingly, of course, this is the basic structure of a mystery/crime drama where Chibnall has had much of his success. I don't think this structure really works for Doctor Who, or at least not if the mystery is uncovered in the kind of dribs and drabs we get here. I suspect a mystery story needs to be upfront a mystery story with the narrative focused on uncovering the mystery, otherwise you get this kind of "why should I care about stuff that happened long ago" problem.