I'd do it too with an extra helper function, but I would keep the first condition out (for readability, flexibility and reuse)

something like

sub cmp_vec  {
   # return either -1,0 or 1 comparing over two equally sized arrays
}


sort { @$a <=> @$b or cmp_vec($a,$b) } @list;
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for full flexibility a cmp-function could be passed as call-back in third position.

As a side note, I'm not sure if this could be done with Perl6 Meta ops, something like @a >>cmp<< @b (after reversing of course).

update

something like

sub cmp_vec {
 my ($a,$b) = @_;
 for (reverse 0.. @$a-1) { 
      if (my $x= $a->[$_] cmp $b->[$_]) {
            return $x
      }
  }
  return 0;
]
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