Something about my past guildies:
There were people that quit wow due to suffering from burn-out or having responsibilities in real life (these reasons also apply to me), but the majority that quit were sick of the lack of content. People were discussing switching to Cata or Legion servers, many guildies went to retail, in order to enjoy the new expansion. So, in my honest opinion the double-reset fatigue pales in comparison to the one of the stale content. Ulduar, as fun it was, became boring at one point. Just imagine what it would be to extend FM's life span to 2 years, in order to enable a single weekly ID reset with an unmodified loot table. Rading one instance for 5-6 months would definitely become monotonous, and people will lose interest in staying. At least, in my opinon.
In my first paragraph, I mentioned the Covid pandemic. Yeah, it's true that FM's initial popularity was influenced by the worldwide quarantine. Since things are slowly going back to normal, then maybe the double reset might not be feasible anymore. I guess that's another thing for the warmane staff to consider, in case they are wondering how to set FM's 2nd season.