Power of the Dark Side too high chance

You have the calculation backwards.  The chance to resist is tenacity-potency, with a minimum chance of 15%.  When potency is higher than tenacity, your chance to resist is at the minimum of 15%.  You would need to have a tenacity of 15 or more above the opponent's potency to start seeing a resist chance above the minimum.  

Slothnado is correct, it's tenacity-potency. So let's assume the base 15% chance to resist, so 0.85*0.70=59.5% chance to stun.

The binomial distribution is:

0 stuns: 1.1%

1 stun: 8%

2 stuns: 23.5%

3 stuns: 34.6%

4 stuns: 25.4%

5 stuns: 7.5%

Please forgive the 0.1% rounding error.

In your pictures, I counted four stuns 3/7 times = 42.9%,

three stuns 3/7 times = 42.9%,

and two stuns 1/7 times = 14.3%

But with such a small sample, your confidence intervals are huge:

3.3% - 82.5% for the cases of three and four stuns, and 0% - 42.3% for the case of two stuns.

In case it's not clear from those confidence intervals, all statistical tests fail. For the cases of three and four stuns, we would need to see it happen 5/7 times before we can reject the null hypothesis (one-tailed, alpha=0.05). Going in the opposite direction for two stuns (since if you surmise that it's getting many stuns too many times, then it would be getting fewer stuns too few times), we would need to observe 0/7 cases of stunning two people before we reject that null hypothesis. So in your pictures, we have no evidence that the stun chance is other than what it claims.

If you have indeed recorded more data, please come back and report for each stun attempt, how many occurrences you have observed for each stunning 0 allies .... stunning five allies. Then we can compare the percentages from the larger data set to attempt to verify your claims.