OK, tks and it's clear enough. Going back to my original question, was it AR's job to draw ref's attention to the high tackle? In this case, has he failed to perform his duty?
Going back to the original question, if it was an AR, he should NOT be watching what the referee is supposed to watch at all if he is "trailing" (i.e. on the other side of the field), but in the scenario as you described it he was in fact "leading" (i.e. the action was close to his side of the field).
A leading AR should never be interested in stuff such as offside, however any kind of foul play that the referee is unsighted from falls firmly under his remit (similarly, the trailing AR covers any foul play behind the referee's back). As such, perhaps it was his "job", but if he failed to spot it - that happens.
It is hard to be a great AR, which is why at the top level there are TMOs to ensure the right decisions get made. I've refereed well over 100 matches, run touch perhaps a factor of 4 times more often (i.e. 500+), and been an official AR ... well I can count them on the fingers of both hands.
In the OP, you also mentioned a "high tackle in the maul". I've experienced players unaware (genuinely) that they were effectively choking the ball carrier in a maul. Two or three seconds of such "choking" is plenty of time to yell "NECK - release" without particularly endangering the BC. An AR can call that too, and only then put his flag out (and call name of referee/whatever signal they have).
