The issue with what you descibe Nihility is the time it takes to cast all that, cooldowns, and cost. Bane = Aethetflow and cooldown so not spammable and also potentially heavily nerfed in Stormblood. Shadowflare = right now cast time, but Stormblood it had a potential 60 second cooldown. Painflares = cooldown, potentially 5 seconds in Stormblood, and Aetherflow. Deathflare = only in Dreadwyrm and at/near end of it. Bahamut = needing to have gone through two previous dreadwyrms.

That all takes time, set up, and aetherflow which you only get 3 to work with till aethetflow is on cooldown. RDM just has to cast and has zero set up and it just costs mana.