An alternative to the ST is a GRT.

In a do block read the data with no line buffering from a filehandle (in this script a HEREDOC) and split into records at points not preceded by start of string (to avoid an empty first record) and followed by the ">>>" which starts each record. Each record passes into a map where the digits preceding the % sign are captured then packed as a 32-bit network order value (logical NOT applied as we want descending numerical order) concatenated with the whole record packed as a string. This is then passed to a simple lexical sort and then into a second map which unpacks the record by skipping the first four bytes which is the number used to sort. The script ...

use strict;
use warnings;

open my $fh, q{<}, \ <<__EOF__ or die qq{open: < HEREDOC: $!\n};
>>> prd1703
Filesystem                                  Size  Used Avail Use% Moun
+ted on
/workspace                                  3.9T  687G  3.2T  18% /wor
+kspace/data
>>> prd1701
Filesystem                                  Size  Used Avail Use% Moun
+ted on
/workspace                                  3.9T  887G  3.0T  13% /wor
+kspace/data
>>> prd1702
Filesystem                                  Size  Used Avail Use% Moun
+ted on
/workspace                                  3.9T  746G  3.1T  23% /wor
+kspace/data
__EOF__

print for
   map { unpack q{x4a*}, $_ }
   sort
   map {
       m{(\d+)(?=%)}
       &&
       ( ~ pack( q{N}, $1 ) . pack( q{a*}, $_ ) )
   }
   do  {
       local $/ = q{};
       split m{(?<!\A)(?=>>>)}, <$fh>;
   };

close $fh or die qq{close: < HEREDOC: $!\n};
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The output ...

>>> prd1702
Filesystem                                  Size  Used Avail Use% Moun
+ted on
/workspace                                  3.9T  746G  3.1T  23% /wor
+kspace/data
>>> prd1703
Filesystem                                  Size  Used Avail Use% Moun
+ted on
/workspace                                  3.9T  687G  3.2T  18% /wor
+kspace/data
>>> prd1701
Filesystem                                  Size  Used Avail Use% Moun
+ted on
/workspace                                  3.9T  887G  3.0T  13% /wor
+kspace/data
[download]

I hope this is of interest.