Devil's advocate for a second, in what might be seen as poor taste so please forgive me.
Drayton Manor Park and Zoo was under independent ownership and a child died. Merlin, for all you hate them, haven't had a death at their parks as a result of ride operation and they own a lot more than one.
I don't think there's ever been an example, under the present Merlin ownership of corner cutting and I think to suggest so is slightly dangerous, disingenuous, unnecessary and potentially libellous. Even with the caveat of "hope I'm wrong".
You could possibly site The Smiler case as an example, down to human error and pressurised targets. This was under different ownership, management and culture though. Additionally you can bet there has been an overhaul in operations, reporting and culpability since then.