Ok, thank you, now I understand the mechanics.The inquisitor have been changed numerous time.
It only remove half the pressure of foreign religion now, or enough to remove one follower, whichever is stronger.
Also it does not apply any pressure itself. You will need a missionary to end the job.
The reason it was changed that way is that is was absolutely too strong and removed any incentive to try to spread your religion, since your rival could erase the work of 3-4 missionaries with a single inquisitor (in the case of very high pressure)
But this leads me to another question - I have tested the missionary in the same scenario, and with spreading religion 5 FR dropped to 3, and MR was raised to 4. So what is the point of using iquistior if missionary is cheaper and more effective? When the iquisitors should be used?