I think that is a very hard line to take, and I would argue - inappropriate at best.
The 57 second timeline, from what I have read, is the time from the pump failure, until the time the raft flipped.
I've seen this style of ride in startup and shutdown, although i've never seen one operating on half it's pumps. I can imagine, given the time it takes the water level to drop in a total shutdown, that the shutdown of only one pump would make the water level drop a much less significant observation.
Basically, with all the water rushing through the station area, guest communications, and mechanical noises, It is doubtful that one pump stopping would be all that noticeable immediately, both from a mechanical noise perspective, as well as a water level perspective AT THE TIME (ie: timeline 0:00)
Also from what we have heard, the main operator panel has no visibility to the unload area, and had no responsibility for that area, which is why there was a separate unload operator. (In later years, Wonderland's snowy could be operated by a single operator using CCTV, with load and unload taking place on either side of the control booth).
It is unfair to be making statements that 'either operator had 57 seconds' to prevent this. Or that they will have to 'live with that'.
Yes, at some point before hand, the water level could have been noticed, the stalled raft at unload could have been noticed - in fact, in both cases, SHOULD Have been noticed - however this doesn't pin it on the operator. For all we've heard so far, Dreamworld's policies, dreamworld's training, and dreamworld's ignorance of previous recommendations brought this about, and in reality, nothing the operators could have done would have saved people by the time it became apparent.
Even the stalled raft may not have appeared 'stuck' but only 'not moving yet' and it may well have been practice on the ride to allow the next raft to 'bump' it along - so even at THAT point, mere seconds before the flip, the unload operator may have not perceived anything wrong, because of the practice of the park's policies.
TL:DR - with everything we have heard, it is not appropriate nor fair to pin the loss of these four lives on an operator, or to suggest that they had almost a full minute to perceive and react to save them. The park's culture appears to have taught them that everything was normal, and only when the raft lifted into the air would they have seen a problem worthy of e-stop, which by then would have been too late.