As my original attempt was so crap, I thought I'd take another crack. Abandoning any attempt at validation and avoiding the regex engine completely, I came up with this which seems to be about 15% better than the best so far.

sub peel {
    my( $s, $n ) = @_;
    my( $start, $stop ) = ( 0, length $s );
    ($start,$stop) = (
        1 + index( $s, '(', $start   ),
           rindex( $s, ')', $stop -1 )

      # reformatting_for_posting error corrected
# Was    ) while $n-- > 0 and index( $s, '(', $start +1 ) > 0;

    ) while $n--    and index( $s, '(', $start +1 ) > 0;
    substr $s, $start, $stop - $start;
}
                 Rate mine-less-lgnt           buk2
mine-less-lgnt  918/s             --           -15%
buk2           1075/s            17%             --
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