Arrow dereference operator question

Based on perlref documentation arrow operator between brackets subscripts
may be omitted so the following code is valid:

@array = ( [1, 2], [3, 4] );
$element = $array[0][0]; # shorthand for $element = $array[0]->[0]


Could somebody explain why it causes syntax error when the above rule is
applied to returned value of a subroutine ?

sub mysub {
@array = ( [1, 2], [3, 4] );

return @array;
}

$element = (&mysub)[0][0]; # $elem = (&mysub)[0]->[0] is valid
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syntax error at testarr.pl line 7, near "]["