just because row 27,895 out of 500,000 was repositioned to slot 3, now 499,998 rows will have their id recalculated.

Not so. Only the ones between the old and new positions need to be recalculated.

sub move {
  my ($from, $to) = @_;
  my $temp = $row[$from];
  if ($from < $to) {
    for ($from+1..$to) {
      $row[$_-1] = $row[$_];
    }
  }
  else {
     for (0..$from-$to-1) {
       $row[$from-$_] = $row[$from-$_-1];
     }    
  }
  $row[$to] = $temp;
}
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