Slicing is superior. Pre-shredded has some anti-caking and other additions that are not cheese. You want cheese and not the convenience and falsehood of industrial shortcuts.
Random suggestions to ignore: Sauté some thinly sliced onions and peppers and the fillings, drain if too juicy and then add them to the cheese. If you're crafty, you can wipe down the pan and reuse it to get a crust on it too by heating the inside tortilla first.
¡Provecho!
I hear you. The evil Walmart corporativa has cheap [$1.50 usd] Cacique brand chorizo hidden by the raw tortillas.
Keep up the quesadilla effort, you are inspiración para otros!