Love a good steak sandwich. From what I have seen in the Philly area, there are 2 cuts of meat commonly used, Rib or Sirloin. I prefer the rib. Then there are 2 ways it comes.
First and most common is shredded meat that is factory pressed into thin sheets that are then pressed together and sold in 10lb cases of varying serving weights by ounces. Usually avail marinated & unmarinated. (Pumped or not pumped)
Second is extremely thin sliced meat from no roll (ungraded) rib or sirloin sub primals . IMHO, this is the best.
Most places use the former because the protein itself is cheaper, the cases stack very efficiently in the cooler & there is no slicing labor or slicer maintenance.
Steakums don't even taste like meat & I think they are mostly a retail supermarket product.