To start, I understand you gain bonus progress in Heresy activities, but I just did a GM nightfall which had about 10 Banes spawn. Of which I killed at least 6, but I gained only 3% progress. Given banes only spawn in harder content, and only about 10-12 spawn per run, your in for a hefty grind. Even of the bonus progress is 2x, that's still at least 10 master runs of the nether or court. That's not even considering if you fail, or if it even counts teammate kills as progress for you.