Aaq, i didn’t hear a reason from rav belsky, and i regret not asking him to explain his shitah. That very determined talmidim don’t need high school is pretty clear; they shouldn’t worry about parnosa, and they don’t need English to not waste time or be more disciplined; I’ve yet to hear another justification for English besides these two factors, which apply to the majority of talmidim.
If HS English is good for the majority because otherwise they’ll waste time and they’re unable to learn the entire day, and they need it for discipline, then changing norms in the working world wouldn’t make a difference. as for parnosa, even if it’s harder to find work without college, having a HS diploma makes it possible to go to college whenever the student wants, but I’ve yet to see any non yekkish rabbonim say that bochurim should be concerned with parnosa when they’re in their prime learning years, even now that it’s harder to get a parnosa without college. Day l’tzara beshaato. Even the yekkies after rav breuer no longer advocate for it, though they have no problem with those who do.