There is no such "aim." The goal is to get as much as possible, while balancing them out somewhat. No, having 15% on a long cooldown does not make Yamaraja a good Hime - it's literally a SR tier buff *cough*Agni has same buff with shorter cooldown*cough*Uuh, no. The greatest asset of Yamaraja is her B frame and her Combo-. But funnily enough, Amaterasu has a stronger B frame and a Blind which does effectively the same thing as Combo- (aka preventing you from getting assblasted by double and triple attacks).It can't hit 7 digits because of damage cap, which is 700k. Hitting 1m damage would require dealing 3.7m damage before damage cap reduction.
In conclusion, how good is Yamaraja? About as good as SR Amon and Agni put together. Is that good? ... well, it's better than a SR, but that's it. Is it something worth EVER Miracle Ticketing, considering there's an actual SSR that fulfills the very same role in the very same element? No. No it isn't.
Ever.