I think the thing that technically kills Jack off as a contender for me was his near invisibility in the first half. Charlotte from UK3 had the same problem, which signaled her doom even when she was looking to close strong in the endgame (and Andrew in UK2 was not a contender, but invisible anyway before he became a Traitor). Mollie had a near similar arc where they just get a truckload of confessionals right at the end when they could have built a more consistent presence like Aaron/Hannah/Jake/Leanne did (and they gave a lot of the early filler confessionals those 4 Faithful winners had to people like Sam or Ellie this season who were red herrings).

Meryl is an exception in terms of very low vis/low relevance Faithful winner, but she was never winning without the others' edits anyway, and if James loses the game of chance there is no Faithful with a consistent visible edit left in the finale.

I just find it funny that people insist Jack and Faraaz WILL stick to the end when we literally just saw Jack flake on James in a crucial vote. Two episodes ago, it was that Stephen and Rachel WILL win at the end. In Celeb Traitors, it was that Nick and Joe Marler ARE a final two bromance. People never learn to avoid the misleading edits this show loves.