I will leave it to other to discuss list operator performance. To remove the undefined/empty element I'd use for and push:

$ cat 669837.pl
# 669837
use strict;
use warnings;
use Data::Dumper;

my @a = qw (onexxx txwxo txhrexe xfourx xxx five);
my @b = ();
for (@a) {
  s/x//g;
  push @b, $_ if $_;
}

print Dumper(\@b);
__END__
$ perl 669837.pl
$VAR1 = [
          'one',
          'two',
          'three',
          'four',
          'five'
        ];
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