Why isn't scavenger Rey any good for sith raid?

I'm currently working on resistance trooper because I heard he was very effective in sith raid but when I asked recently about using him to replace finn I was told to replace Rey instead. Why is she not any good? Finn was downgraded pretty badly since his lead rework and as a tank I'd assume his damage isn't all that great compared to Rey who was once considered to be a glass cannon. What am I overlooking?