I just realized this, despite reading and listening to Dr Heiser on this topic and passage multiple times. Did I just overlook it, or has he not put the passage this particular way before?
This passage references all three of the divine rebellions, the three reasons why humanity is so corrupt according to a Second Temple Jew (as Dr Heiser would put it) – sin from the Genesis 3 fall (suffered once for sins), the corruption by the Watchers of Genesis 6 (the spirits in prison), and the mismanagement by the gods over the nations of Genesis 11/Deuteronomy 32:8/Psalm 82 (angels, authorities, and powers):
For Christ also suffered once for sins, the righteous for the unrighteous, that he might bring us to God, being put to death in the flesh but made alive in the spirit, in which he went and proclaimed to the spirits in prison, because they formerly did not obey, when God’s patience waited in the days of Noah, while the ark was being prepared, in which a few, that is, eight persons, were brought safely through water. Baptism, which corresponds to this, now saves you, not as a removal of dirt from the body but as an appeal to God for a good conscience, through the resurrection of Jesus Christ, who has gone into heaven and is at the right hand of God, with angels, authorities, and powers having been subjected to him. – 1 Peter 3:18-22
See also the essay ‘1 Peter 3, A Trifecta of Hope in Christ‘ at https://scottthong.wordpress.com/2021/09/29/my-theological-essays/