To be honest, 80% effectiveness for a generation 2 of a long term drug is a pretty nice value, especially in this field and the regulatory mechanisms it affects.
That's better than basically most psychiatric, antivirals, antihypertensive and antidiabetic medication.
Only a few long term drugs like contraceptives, some chemotherapeutics and some hormone replacement drugs work that well in that many cases. And most of them are not Gen 2 drugs in a new field.