You don't co-opt B::Concise for this. You use B::Utils::walkoptree() and everywhere you find a B::LOGOP, you increment your complexity by one. You shouldn't actually use this, however, for points better raised by BrowserUK, simonm, and stvn in other parts of this thread.

use B ();
use B::Utils ();
print "function() == " . sub_simplistic_complexity( \ &function );
print "overall: " . program_simplistic_complexity();

sub program_simplistic_complexity {
    my $simplistic_complexity = 0;
    for my $op ( B::Utils::all_roots() ) {
        $simplistic_complexity += op_simplistic_complexity( $op )
    }
    return $simplistic_complexity;
}

sub sub_simplistic_complexity {
    op_simplistic_complexity( B::svref_2object( shift() )->ROOT );
}

sub op_simplistic_complexity {
    my $op = shift;
    my $simplistic_complexity = 0;
    B::Utils::walkoptree_filtered(
        $op,
        sub { shift() -> can( 'other' ) },
        sub { ++ $simplistic_complexity } );
    return $simplistic_complexity;
}
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