Thanks for putting in the effort to test my wild guess (++).

On my machine, Your test gets me 2174 echo per second, which is around 460 MICRO seconds each - yes , still not in NANO seconds.
(It helps that I am writing to an SSD disk)

I updated the code slightly to get closer to the "echo" open/close of the file, and append to it, and 10x the iterations:

use strict;
use warnings;
use Benchmark 'cmpthese';


cmpthese (100000,
    {
        'print' => sub { 
            open my $fh, '>>', '/tmp/wp.txt' or die $!;
            print $fh "x\n";
            close $fh;
             },
        'echo'  => sub { system "echo x >> /tmp/we.txt"; }
    }
);
exit;
[download]

This gives me:

          Rate  echo print
echo    2168/s    --  -98%
print 140845/s 6397%    --
[download]

Where the perl performance is pushing the limits of nanoseconds, at 7100 nanoseconds per write.

In any case, the lesson learned is that perl is about 70 times faster than "echo".