My Fluri is 6* and maxed on runes, but her gear is probably pretty pedestrian compared to the higher end players here. Here she is:
She's probably my favorite tank on my roster. I never knew how she was pre-nerf, but I find her extremely useful postnerf, both in PvE and PvP. She's my queen tank in raid, and my G11 tank/defense breaker. Carmin is probably stronger defensively, but I find Fluri more fun to use, so I use her way more often.
In PvE her defense break is always useful, and her passive heal + minor CR pushing is pretty decent over time. Her speed means she procs that passive heal quite often. She's tankier than she looks too, thanks to her passive barrier.
In PvP, her S3 is great as a way to lock down a key target from using their S3 (because of provoke), or as a way to kill someone fast with defense break. I don't regularly use her in GW, but I pull her out now and then if I need an Aurius user.
There's a bit of rng in the fight in that sometimes you just get screwed if the wrong person gets stunned, so it might take a few tries until the boss doesn't stun anyone critical long enough for you to kill it.
It might also help to have not be too reliant on one damage dealer, and have at least another unit be capable of doing enough damage to at least kill an add. I find having Seallona built for a bit more damage helped a lot, because her S2s and S3s served softened the adds over time, which helped when I needed to kill something to free someone. Or save an Arky to help in those cases.