Did a bit of a deeper dive. I have years of logs, so I can simply check how often I am getting bashed, stunned and kicked. This data is from 2018 to present.
In conclusion there is a 70% chance to be bashed per bash/kick attempt, and a 20% chance to be stunned on a bash hit.
Bashes landed 70% of the time, so the total chance of being stunned per bash/kick attempt is 14% (20 x 0.7) while the mob is unslowed, every 8 seconds.