But there should be no problem passing a reference to an arbitrarily complex data structure ...

Well it's insofar a problem that it's more complicated and unintuitive. Would you preferre to use HTML this way?
    <tag="a" name="anchor" ... >
"There should be no problem" to use a workaround is good argument to abandon Perl for the sake of a more primitive language.

But if you consider the Perl "named parameters" alternative to lengthy positional argument lists in function calls (especially where defaults may be involved) to be a complicated and unintuitive workaround, then just don't use it! It's a perfectly valid choice. (However, you may not have much luck in seeking for a solution among "more primitive" languages: I think few, if any, such languages offer anything other than positional function argument lists.)

Me, I can perfectly imagine a case where I'd like to pass anonymous functions with parameters (e.g to use as defaults):
    doit ( \&func1 => [para1, para2], \&func2 => [para7, para4] )

True, if you go anywhere near a hash with that argument list, you will stringize and therefore completely destroy the function references. So, don't do that!

However, consider this example, and consider what it would take to implement it as a function with a pure positional and possibly defaulted argument list:

use warnings FATAL => 'all';
use strict;

doit({ func3 => [ \&up => [ qw(x y z) ] ] });

sub doit {

    my %defaults = (
        func1 => [ sub { print map $_ . '1', @_ }, [ qw(a b)   ] ],
        func2 => [ sub { print map $_ . '2', @_ }, [ qw(c d e) ] ],
        func3 => [ sub { print map $_ . '3', @_ }, [ qw(f g)   ] ],
        );

    my %args = (%defaults, %{ shift() });

    for my $func (qw(func1 func2 func3)) {
        die "unknown func $func" unless exists $args{$func};
        $args{$func}->[0]->(@{ $args{$func}->[1] });
        print "\n";
        }

    }

sub up { print map uc, @_; }
[download]

Output:

a1b1
c2d2e2
XYZ
[download]

Again, it's a matter of personal preference: I know what looks better to me.