I think there's some misunderstanding on what T5 RA positions mean.
T5 refers to top 5 schools - harvard, mit, stanford, chicago, princeton (there may be disagreement on which are considered top 5).
Anyways, full-time RA positions are generally good for people who feel that after 4 years of undergrad, they don't feel confident about their CVs to apply directly to gradschools (for example, lack of research experience), and for those who just don't have the money for masters programs (like myself). So the time spent as an RA acts as a buffer period.
For students who are geniuses and have excellent records, no need to waste time working as an RA before gradschool.
There are 3 full-time RA options, and each have pros and cons.
1) RA at T5: may be ideal for those whose undergrad institutions are not one of the top schools. direct access to top-professors, will have excellent LORs at the end if they perform well. + you can take advanced courses at school, which also increases your chances of getting into top programs.
2) Fed: may be good for those who want a more sense of working at a corporate. when you work at schools, you may still feel like you are a student, whereas when you work at the Fed, you will feel like you actually have a proper job.
+ tuition supports for RAs who take classes at nearby schools (may depend on location, also there just may not be any good schools nearby, like Richmond for example)
+ city life (for places like NY, Boston, SF..)
but, depending on where you go, and which division you are placed into, you may work with somewhat mediocre economists, so the letters from them will not look as awesome as the ones you might get from T5
3) Other research institutions such as NBER, IMF, etc.
similar to Fed
Hope this helps.