For those following the posted guide, the video for the final boss fight is different for Tier 1. I recently ran with Dadi’s group on a T1, and the fight was quite straightforward and more stationary. The guardian was able to take the Gloom to the very top of the stairs and sit with him there the entire fight. The rest of the group then stood in what had been the Gloom’s starting spot for the entire fight and worked adds in a very measured and specific way.
I wouldn’t be able to fully describe it here, but in practice it is quite easy to manage. There is not so much running around as in the video. People need to know which of their skills are interrupts and seriously spam those at certain times, and a couple of ranged hitters really help. The guardian needs to be savvy about keeping his health up while dealing damage on the Gloom as much as possible because the rest of the team is focused on adds.
I would be willing to go with a T1 team to show this technique, if it every becomes a kin project.