the problem is maybe right now Amon's status protection can be usefull, but she is fire attribute and supposed to face wind attribute which does not have alot, or any debuffs (correct me if im wrong, idk if future wind raid bosses spam status debuffs). Cassiopea's skill is amasing because u can throw light weapon at her and make her face dark raids that spam statuses. As for self debuffs. Again, main sourse (or only source, im not sure here) is dark kamihime (tsukiyomi, beelz) and the thing with dark himes is... theres plenty of amazing choices that are much, much, much better than Amon (Bastet, Nyarlathotep, Pale Rider, you name it). Even worst dark hime is better than takin amon in that slot.
on the off note, main point of Tsukiyomi is making your team blind - that allows you to prolong fight and get an extra snatch or 2. since theres plenty of blind sources that dont involve you blinding yourself, i dont see any point in using Tsukiyomi for any other reason than to blind yourself for that very reason.
ony one situation i can see her bein usefull is in party with Ares, since she has atk buff that sets her on fire, so maybe you would want her there... but seriously, im looking through fire SR himes and dont see any reason to pick Amon over ANY of them. Unfortunately we only have Agni and Bryn now, so no other choice than to wait...