UE ultimates can get really long if you're soloing them, just by nature of their ever growing HP. And if the idea of having to solo a demon fight is foreign to you, then you don't know the struggle of hanging around rank 100 :P
Like the last time we had Envy, I think ult fights in the 100-110 area took me 40+ turns.

Acala is 'worth' awakening in the sense that it actually does move her up a tier or two. The thing is, base Acala starts out at 'come off the bench at best' tier* due to being lackluster for an SSR at her role (that's the nice way of putting it). For an SSR, she was one of the worst possible ones to roll. Awakening Acala makes her actually good at fighting raging enemies, like she was ostensibly designed to do. It raises her to usable! You no longer have to hate yourself for rolling her! And in your case, she automatically gets a starting spot over Yamaraja when fighting wind catastrophe or Lust.

*assuming a decent selection of SRs to work with. The last time I used base Acala as a starter was when I still had to piece my fire team together from R's