I understand what you are saying and all is good. I dont disagree as posted I have a HP on the second floor, rarely used but its there.
But the efficiency isnt there at those temperatures, maybe better said, measuring the supply vent temp isnt an indication of efficiency.
I suspect you know the difference but many people doing it in that method may not even know there are (back up) aux. heat element coils for when the heat pump cant produce those 99 degree temperatures so they maybe thinking the heat pump is doing it when in fact its just standard electric coils doing the job.
From my electric bill: Summer AC set on 68F and winter heat set on 64F:
Difference 2021-2021
Nov 2021 - 1571 kWh 56 kWh/day - $219.94 $35.28
October 2021 - 1715 kWh 57 kWh/day - $240.10 ($18.48)
September 2021 2219 kWh 67 kWh/day - $310.66 $4.48
August 2021 2001 kWh 66 kWh/day - $280.14 ($96.88)
July 2021 2127 kWh 68 kWh/day - $297.78 ($118.44)
June 2021 1936 kWh 60 kWh/day - $271.04 ($80.64)
May 2021 1180 kWh 42 kWh/day - $165.20 ($23.10)
**New HP system was installed**
April 2021 - 1572 kWh - 47 kWh/day - $220.08
March 2021 - 1505 kWh - 51 kWh/day - $210.70
February 2021 - 1685 kWh - 52 kWh/day - $235.90
January 2021 - 1436 kWh - 47 kWh/day - $201.04
December 2020 - 1442 kWh - 49 kWh/day - $201.88
November 2020 - 1319 kWh - 50 kWh/day - $184.66
October 2020 - 1847 kWh - 53 kWh/day - $258.58
September 2020 - 2187 kWh - 75 kWh/day - $306.18
August 2020 - 2693 kWh - 99 kWh/day - $377.02
July 2020 - 2973 kWh - 82 kWh/day - $416.22
June 2020 - 2512 kWh - 54 kWh/day - $351.68
May 2020 - 1345 kWh - 48 kWh/day- $188.30
November 2020 I averaged 6.2 gallons/day of oil used and at today's price that cost $576.60 for the month (Ave temp 44.6F)
November 2021 I averaged 4.2 gallons/day of oil used and at today's price that cost $390.60 for the month (Ave temp 40.5F)
So the heat pump costs me $35.28 more in electricity but $186.00 less in oil. Average low temp November 2021 was 31F. I will update when December numbers are in.