Its probably dependent on a recessive trait. Take punnet square for example, we can use it to figure out the probabilty of genetic variance of a living being in a very basic level. I'd say the blood purity is a recessive genetic trait which TW formed after becoming a god. So higher blood purity means you possess the 'desirable trait' of a god. A person far off down their family tree can possess a trait lost over the years due to his ancestors marrying into different families. Say your great grandfather had red hair and great grandmother was a a brunette, dark hair is a dominant trait whereas red hair is recessive. Thus your grandfather was born with darker hair and your father was also born with dark hair.. Luckily or unluckily you manage to be born with red hair. the family's red hair skipped 2 generations. Its just probability. The red hair trait is always there, just very low chances of it becoming your forefront trait. Its the same with blood purity i reckon. Its all luck. Ruo having 98% doesnt mean he's more like TW, it just means he got lucky. That's not the case tho with Wu Heir, They are TW. What Wu Heir has from birth, the others prayed just for a drop of.
