Subjective viewpoint:
+ The controller did not even ask for an expedited departure.
+ Even if a rolling_and_expeditious takeoff had been executed, the normally-expected LoViz separation standards could not be re-established. The breach of reasonable spacing was already done with the line-up instruction.
Telling a crew to line up and then advising there's traffic closing is sloppy work. What about (instead): "There is 767 approaching traffic at 3 NM. Are you ready for an immediate departure?" Despite that still being a completely unacceptable plan to propose, that may have helped the SW crew to decide well and stay clear of the active.
Pilots are drummed to understand the difference between ATS and ATC, and the different levels of service and responsibilities that are eventually taking place. If you think of it, from what has been reasonably established to be factual, there was no _controlling_ taking place at all.