Well 6 out of 7 is a good percentage especially when one of those examples came from the mouth of God Himself out rightly.
You really aren't understanding the numbers. I will take the blame for that as I really didn't think I explained it that well.
6 times out of 42 times where the word "minister" is used in the Bible it DID NOT refer to a member of the clergy.
Twice it called Joshua the minister of Moses. Was Moses a spiritual leader or a political one? I would say both, so these two are in doubt. But Joshua (at the time it is referring to) was NOT a public minister in the way Romans 13 is speaking of. He was not Israel's minister; he was Moses'. This was at the time when God himself chose the leader and not the people. That changed when the people asked for a King (Samuel and Saul).
The third and fourth are King Solomon's ministers who again weren't serving the public directly like in Romans 13. They are accounts of the same thing. One is from the book of kings, the other from Chronicles. I am being kind here because the first 4 are really only 2 in that it is repeated information. Also, 2 of them are in doubt because we have to wonder if Joshua was helping politically or spiritually.
Number 5 is speaking of the ministers of Satan, so frankly, its still a spiritual matter. The 6th is a rhetorical question asking if Jesus is the minister of sin.
So its really 6 out of 42. The other 36 times it is clear a "minister" is a member of the clergy. Now of those 6, two are questionable and repeats, 2 are repeated verses, one is a rhetorical question and the other is talking about Satan's ministers.
So you noted 6 out of 7. Where did the "seven" come from? 7 times a variation of the phrase "ministers of God" are used and ALL 7 times its talking about clergy. Romans 13 calls them the minister of God and EVERY TIME that phrase is used or a variation of it is used it is talking about a clergyman.