LF an addon which would calculate KP.
The concept of KP is entirely "feelycrafting", and not an actual accurate representation of anything.
Killpoints.
Is a theory going around that you can math out the odds of receiving a legendary based on killpoint "scores" awarded from various types of content.
With any such theory though, there are people held up as "proof" when they fit the pattern, and those which do not are dismissed as "RNG".
I think it was a bit different,
I think (if i remember correctly) it went as follows:
At release:
There were quite large diminishing returns on legendary droprates, getting worse the more you had.
There was a bug that if you had the luck to get one legendary, for the first few weeks the diminishing returns didn't work correctly and you actually had a improved chance to get your 2nd/3rd legendary (this was fixed 2-3 weeks after release iirc).
7.1:
Buffed the droprate for Legendary 1 and 2, but still kept the diminishing returns for legendary 3 and up, whilst 3 and 4 were relatively Ok still, 5 and up were a huge grind (unless lucky)
7.1.5 (or shortly after 7.1.5):
Diminishing returns for legendary 3 and up were removed. Making it so that 1 and 2 have a increased droprate compared to release and 3 and up all have the same base chance to drop.
As some point the community brought up the KP system, , which actually seemed quite accurate (for example we ran all 110 mains trough it in our guild, around 70 characters raiders and socials combined), and it had about a 95% accuracy in that sample size. Alts were less accurate due to some stuff in the KP system being counted from the first moment a character on a battle.net account got a certain achivement (i think it was the reach 110 achie).
At moment it should be like this:
1. Base odds should be the same for 3rd legendary and onwards
2. Effort is RNG as you can still be lucky and get legendary 4 and 5 within the hour (when extremely lucky). But on average you should see long term that each legendary above 3 requires about the same effort in content done.