Rather than debate when to be looking inside at a TAS how. about we start with asking questions about how many "Alerts" or other advisories would be triggered on such displays during the time period leading up to this collision.
How many airplanes and helicopters were airborne or on the ground and close enough to generate an indication on TAS or other traffic warning systems?
Would there enough to saturate the system and thus render them to be more a distraction than an aid?
For flight operations being conducted by the two helicopters....at what distance would other traffic not be seen as a conflict and how would you a Pilot be able to minimize warnings that did not constitute an actual conflict.
Would a Pilot be prone to turn the audio down to prevent having the audio alerts interfering with radio calls by other traffic?
Technology is grand but sometimes it proves to be a distraction rather than an aid.