When you get used to the way functions work with lists, you might start writing it more like the following.
(Then again maybe not; it could be that I'm just really used to doing code golfs.)

    # calls .fmt on each array which then calls .fmt on the elements
    # the results of which are implicitly joined with a space
    # print the result with trailing newline
  .fmt("%7.1f").put for @arr;

      # if it must be tab separated
      # $_».fmt("%7.1f").join("\t").put for @arr;

    # repeat '=' as a string 7 times, and list repeat that
    # coerce to Str (space separated) and print with newline
  put '=' x 7 xx @arr[0];

      # if it must be tab separated
      # put ('=' x 7 xx @arr[0]).join("\t");

    # add the values in the columns up and format them
  put [Z+](@arr).fmt("%7.1f");

      # if it must be tab separated
      # put [Z+](@arr)».fmt("%7.1f").join("\t");
[download]

At the very least I wouldn't use loop for most purposes, as it's easy to get off-by-one errors and to accidently mutate the iterator variable in the block. Also the iterator variable in a loop construct is scoped to the outer block, not the loop block.

  for @arr -> @inner {
      for @inner -> $_ {
          print .fmt("%7.1f\t");
      }

      put(); # use the value of $*OUT.nl-out
  }

  ...

  for [Z+] @arr {
      print .fmt("%7.1f\t");

      LAST put();
  }
}
[download]