Subpar performance is a huge drawback of Perl 6.

I usually don't program in Perl, but occasionally use it instead of sed.

Compare, Perl 5 vs. Perl 6:

    $ time yes | head -n1000000 | perl -pe 's/y/n/' >/dev/null

    real	0m0.945s
    user	0m0.944s
    sys	0m0.016s
    $ time yes | head -n1000000 | perl6 -pe 's/y/n/' >/dev/null

    real	2m49.881s
    user	2m44.892s
    sys	0m2.184s

Spending several minutes to do what can be done in under 1 second is just unacceptable.