I suspect that the optimizer is just removing the whole $foo bit from "stupid" for you.

I was wondering if $a->[1] would be much faster than $hash{$a}{this}. I didn't think it would be by a big enough factor.

If you want raw speed here, create a side array for comparison and sort a list of indices:

my @list= keys %hash;
my @sort= map { $hash{$_}{this} } @list;
my @sorted= @list[
    sort { $sort[$a] cmp $sort[$b] } 0..$#sort  ];
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