And you know this because you've seen it happen? In NL, pre-selection happens at 12 years but actual specialisation doesn't happen until 15 years old. That's three years for children to switch tracks, try things and see what works best for them. And even then, students can pursue an upgrade track after graduation that would still grant them access to university at the cost of an extra year of secondary schooling (which also gives them an extra year of maturity, which often also helps).

I don't know how it is in the UK, but your comment strikes me as a typical boogieman from someone who hasn't actually seen the system in action.