In re of sarcoids, listen to your vet. My minimal experience (two separate incidences, managed with the “leave-it-alone” method) with sarcoids has found leaving them alone to be best, generally.
For dull coat and fur-less patches, re-evaluate diet for necessary amounts of vit/mins. Also, consider a de-worming protocol if you don’t already have an active one (fecal counts can be very enlightening, and cheap!).
Where sarcoids can be slow growing and benign (and your vet is already aware), I would address the dull coat issue directly.
Sure there's right and wrong but mostly there's just a whole lotta different.