half a day to type

You keep dwelling on that, but I think you're misdirecting. He wrote, "spend half a day writing and debugging code", not "half a day to type in one line".

If someone has a bug they need to track down, they're far more likely to waste cycles on a line like $_=do{local$/;<>}; than one like $_=read_file($file);

Now let's compare apples to apples:

use File::Slurp;

my $text = read_file( 'filename' );
[download]

vs

my $text = do {
  local $/;
  open my $fh, '<', 'filename'
     or die "Error opening filename for read - $!";
  <$fh>
};
[download]

For most programmers, the former looks sane.