No, it’s literally you who isn’t getting it. The fact that you mentioned group ratio and saying that there’s always a tank in the run is proof that you don’t comprehend this.
If we look at DF S4 and apply the same formula we get 2.92. If your argument was right then it wouldn’t be off by .12 when the gap between DF S3 and TWW S1 is .02.
In DF S3 each tank ran ~161 keys in the season on average.
TWW S1 each tank ran ~93 keys in the season on average.
This actually points to there being more tanks, not less.