You seem to be failing to take into account the fact that English speakers of age 10+ rarely ever refer to their siblings by "bro," "brother," "big bro," etc. Whereas this is -very - common for the Japanese, especially when being respectful. In other words, it's a fine literal translation, but its meaning and use usually doesn't match up culturally and therefore isn't that good of a translation.
I agree that there are generally ways of working around it(for example, in translating -sama, you can just make the character speak politely or something), but I disagree on the point that the presence of some untranslated Japanese makes a translation worse. Partially. You're correct in that translations you make for retail should be localized for the general audience, but they won't be as accurate and close to the original as translations for a fan community will be, because the fan community is more in tune with the original language and thus you don't need to fudge as many things that have no highly accurate translation in English.
So the question of what makes a better translation should take into account who you're translating for.