I usually have issues with condensing my paragraphs but you'll lose readers just through intimidation.
JTR is still an absolutely amazing team through tiers 1-6. On tier 7 no health reduction so there's nothing new with a JTR team there. my guild went up 1 (almost 2) tier levels. So complaining that JTR is under performing when all it would do is just dominate the whole raid is ridiculous. It shouldnt take 1 team that was out from the start to beat a new raid, Power-creep allows for this but allowing it from the start doesnt make sense game design wise
You mentioned deathmark. yes it does more damage, but it has no turnmeter synergies like with the resistance faction. And attempts to abuse it led to Chexmix, which requires lots of effort to get right and wouldnt just win the raid with 50 of them.
Advice before "nerf" invest in JTR. after "nerf" invest in JTR as its still the best overall team. And when people come to heroic they will still need her.
As for any damage argument. halving the health would halve the expose. But it wouldnt halve the actual attack damage. This means that the damage number you do at the end of the fight will be a higher percent than before. This has been thoroughly explained by other people but you seem not to be listening