think you are right in your approach when you say that depending when you acquire the second language you will have different types of bilingual (simultaneous or sequential). Anyway, in the cases that you raise, we are talking about early bilingualism and in both cases the L2 should be learned before the end of the critical period of acquiring a language. So in both cases the child would achieve the competence of a native speaker in both languages.If your concern refers to the future, the key will be the time and quality of exposure the child receives in each language. The community and environment of the child will play an important role; keep in mind that if you don’t speak your L1 the language proficiency can considerably decline.So we can say that becoming a better speaker is not only conditioned by when the languages are acquired, but the exposure time we have in each of them.