...but also produces an extra line that is empty.

That is due to your trailing \n and has nothing to do with the parenthesized $_,<> - compare

echo -e '55\n44\n33\n22\n11\n' | perl -n -e '@a = ($_,<>); END{ print 
+@a; } '
echo -e '55\n44\n33\n22\n11' | perl -n -e '@a = ($_,<>); END{ print @a
+; } '
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- because echo -e will add a newline to its argument, so there are two of them, and thus an empty line. Use echo -en to suppress that:

echo -en '55\n44\n33\n22\n11\n' | perl -n -e '@a = ($_,<>); END{ print
+ @a; } '
[download]