This model only works if the away teams are the most competent people you have. Generally the “loaning” business is a cowardly way for teams to trade the worst engineers you have (bonus point if that engineer is someone who everyone praises but is secretly shit and only the manager knows that reality).

I've only gotten completely new hires as loans, where you also have to train them up to being useful

I don't see how having Away Teams fixes this issue. The Away Team member is still free to write shitty code (or un-write good code, as in this case), and it is still the responsibility of the home team to catch that in code reviews.