Your understanding about how the cpu's for ipq806x should work has increased considerably over the past 2.5 years.
If you have not already done so, try looking back at what we did trying to understand what changed wrt cpuidle between 4.14 and 4.19. In particular, this post and a few below that.
Given your observations above, it sounds like the "past fix" might only be appropriate for 8064 cpu's and not 8065. It seems like something more sophisticated is needed to properly enable cpu idle for both 8064 and 8065 cpu's.