that's why Mexico has "tortas" you dumbasses!
it is possible for a culture to have more than one of the same thing. Its like arguing that linguini isn't pasta because the Italians also have spaghetti which is already pasta. if anything the fact that the culture has sandwiches would lean very heavily into the possibility of a taco being a sandwich as that already exists in the culture and isn't some new/unique or standalone item.
I don't think the substance of the taco shell matters either. Sandwiches aren't stricting made from one grain either. There is cornmeal sliced bread. you also have potato bread, so on and so forth. so a corn vs flour tortilla is a little irrelevant. both sandwich "bread" and taco "shells" are processed thru similar means. a plant based base is ground up, water is added, its mixed and prepared a certain way with the application of heat.
for me the discussion comes down to what makes a sandwich a sandwich. it is the fact that there is a filling carried by some other media as part of a singular entree. The carrying media isn't fully enclosed, it has similar fillings (meat, cheese, maybe some type of greens). and that if you were given the filling to either a sandwich or a taco without the bread or without the taco shell you wouldn't call either a taco or a sandwich. the type of fillings aren't set, only cheese like a mozzarella STICK, or only meat like a corndog. the carrying media being open allows both to be seasoned or filled as liked, with the addition of condiments acceptable on both, including more crossovers. and it isn't something like a food "bowl" which fully contains a liquid. It isn't mixed together like a pasta, sandwich and taco the carrying aspect is always separate from the fillings until consumption. and without the fillings you wouldn't consider bread a sandwich nor a taco shell a taco.
the ability to apply a filling from either to the other and still be relevant as a "taco" or a "sandwich" says they are considered the same. like if you took a BLT, lost the bread, put the bacon, lettuce, and tomato in a taco shell, ate it like a taco, you would call it a BLT taco. which sounds pretty dang good. take your choice of taco meat filling, cheese, shredded lettuce, and put it on sandwich bread, and you have a very good sandwich.
I think this is a case of all squares (tacos) are also rectangles (sandwich), but not all rectangles (sandwich) are squares (tacos). so a taco is a sandwich.
anyone who disagrees with me is clearly a Joedawg level Georgia fan who enjoys sniffing other dude's balls.