Yes, the tech's input is questionable at best. Alignments and opinions are best served from qualified independent shops not your local "all makes" service centers. My son works at a large West coast tire dealer (Les Schwab) that will not align BMW's or any lowered cars due to policy, warranty and liability reasons. He points out their computer provided alignment data is often wrong where they maintain "cheat sheets" of correct specifications. A proper 4-wheel alignment should run about $150 and they should identify your tire issue if alignment related.
You should clearly know if you're so low that you're scraping the fender liner from obvious scraping sounds and gouge like wear.
I had a cupping issue on the front, outer edges with brand new tires. The dealer explained it was a "common BMW issue due to the camber specs". I fought hard to get this resolved. Turns out it was the tire (Yokohama S Drives) where after the same size tires (Toyo Proxes 4) were installed, the problem disappeared. The car was inspected at no charge for alignment. The dealer was truly puzzled as they've installed Yoko's on many other cars without this occurring. My point is, most dealers are not purposely idiots or out to chase away business with incompetence, they just don't have vast experience with our cars.
Anything made can be made Better