I have two main points to make...

1. The test's difficulty is individualized.
2. a candidate's death is accidental.

When reading Moiraine's PoV in NS about the test to become an Aes Sedai, one wonders how anyone else can pass it and gain the shawl. After all, some Sisters aren't as confident as Moiraine, and none are as powerful as her. When one looks at the test, it seems that the candidate is distracted by something to prevent them from weaving the desired weave. Sometimes the weave is useless, but sometimes it can be used as a solution to defeat the distraction. However, if one looks at Moiraine's test against the Trollocs - it's a wonder that anyone else can match that. Moiraine, being the strongest woman in the Tower, wove her target weave but also split her flows to weave fireballs and lightning to kill the attacking Trollocs. She even admits that some of the Trollocs died right at her feet, showing how close they came to killing her. Moiraine wasn't at her potential at this stage, but it's reasonable to assume that other Sisters aren't at theirs either when they test.

Even if they were at their target strength, how could a weak Sister like Daigian or Cabriana pass the test? They certainly don't have the strength to counter the same force that Moiraine did, and she was hard-pressed. The wounds sustained in the test are real, and death is therefore real too. On the other hand, a trained woman like Nynaeve or Elayne would easily walk through the test considering they can split their flows so many ways, and command such a great amount of saidar. A group of Trollocs would be annihilated by a very powerful woman like Nynaeve.

We already know that the Sisters who power the ter'angreal determine the tests themselves, most likely on a rotational basis (Elaida creates a nasty test for Moiraine which includes her father). It seems reasonable that they would push someone like Nynaeve with a much larger amount of Trollocs, for instance, to create a dilemma for her and see if she can channel under stress. The difficulty of each test would increase until the commanding Aes Sedai felt that the candidate was hard pressed to pass. A weak candidate like Daigian would face maybe only two Trollocs, even though this would be enough to cause her a great deal of stress while she tried to weave the desired weave.

Similarly, it is likely that all deaths in this ter'angreal are accidental and cannot be prevented by the commanding Sisters. It is likely they try to prevent or even stop a death if they see it coming. The Tower considers the loss of a candidate to be a great failure on their part, but it unlikely they allow a struggling candidate to die. Most likely they try to unravel the challenge before it harms the candidate, but sometimes they only have moments e.g. before a Trolloc hacks the candidate to death, and sometimes the Accepted is lost.

The test is therefore individualized to the Accepted. Nynaeve would face a very tough opposition, and Daigian a small one - but both would be equally pushed to their limits.