The exact duties performed are not as important as the duties they are able to perform. It is not necessary that they actually perform them, only that they are eligible and qualified to perform them.
Sounds like the guy had bad counsel.
I had a case where a lay pastor who never attended seminary qualified as clergy for sec 107 as the lay pastor had actually given sermons, communion, and most of the functions of the senior pastor.
I’ve been away from this for quite a few years, but welcomed your points as I am in the process of starting a church and needed to refresh. I just pulled out the IRS clergy audit guide and was doing a refresher. I performed one sermon per month prior to relocating and held weekly study sessions. Now I travel doing evangelism work.
The substance vs. form issue goes a lot deeper than just the tax laws. In some states, the definition also determines who is eligible to perform marriages. In Pennsylvania, there are restrictions. Rather than file for divorce, some parties are asking for annulment as the marriage was not legal due to the pastor not being eligible to perform the marriage service. Pa. did away with the common law marriage about ten years ago.
May God bless your ministry.