F/+ is a combination of FEI and SP+

2016 - 66 O, 33 D
2017 - 120 O, 61 D
2018 - 71 O, 45 D
2019 - 68 O, 64 D
2020 - 3 O, 11 D
2021 - 7 O, 84 D
2022 - 19 O, 53 D (so far)

This season is still early and the numbers could still change drastically. Overall I would say the defense has been up and down alternating decent years with sub-par years.

Also, it's interesting to note that during Kalani's first 4 seasons the Defense actually outperformed the offense. Then in 2020 both were elite. It's only been the last 1.5 seasons where the Offense has been great and the defense has been mediocre.

I'm not saying that we don't have a weakness on defense. Just pointing out that it's not as bad as some want to make it out to be. You claim that BYU's defense should be ranked in the 40's on average. According to F/+, from 2016-2021 (not including this year since it's not complete yet) our average Defense ranking is 49.6 (compared to 55.8 for the offense).