Your custom sorter should use $a and $b as the inputs. If you wish for the arguments to be passed via @_, you need to use the ($$) prototype. I believe this is slower.

In fact, your whole approach is complex and slow. Fix:

my %term_order;
@term_order{qw( SM AU WI SP )} = 1..4;

my @try = (
    [qw( WI AU SM SP )],
    [qw( SP AU SM WI )],
    [qw( AU WI SP SM )]
);

for my $try (@try) {
    my @sort = sort { $term_order{$a} <=> $term_order{$b} } @$try;
    print "@sort\n";
}
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SM AU WI SP
SM AU WI SP
SM AU WI SP
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