I had this same problem when making my own pizzas, and it bugged me a lot. I work at papa john's and I was trying to figure out why my home pizzas had dry "hardened" melted cheese. It would all pull off in one bite, and now I shall share what I have learned.
its not just about quantity of sauce. at PJ's, we often use too much sauce or someone will order extra sauce. Usually, we add more than we are supposed to because we think we are making the customer happy. The cheese on these pizzas does not usually slide off. Unless:
If you order a pizza with tomatoes or pineapples, we often do not have time to fully drain the ingredients. All this extra juice adds water to the crust and sauce. And herein lies the problem.
Our sauce is very thick compared to a cheap pasta sauce from walmart. When I make sauce at home, I take a can of delmonte garlic and onion pasta sauce (99 cents) and add another pasta sauce to it. The Del Monte is too sweet but i like the flavor. So I get another can of something less sweet. I kept getting inconsistent results unless I used less sauce, as you all pointed out. But the amount of sauce is not the problem. Its the wetness of the sauce, and the wetness of the dough. Also, you need whole milk mozzerella, better to shred it yourself.
I add 2 tbsp of olive oil to the sauce and reduce it. The sauce will be thick enough when the oil no longer separates. It should be "pulpy"... not like chunks of vegetable matter, but it should look grainy and uneven... When the sauce is thick enough, the oil will incorporate into the sauce almost magically. If you still see a sheen, reduce more. of course, if you add too much oil it will never incorporate.
There are storebought sauces that are the right thickness, but they taste terrible because there's usually a strong but stale tomato and herbal flavor. The flavor changes the more its cooked and I guess when it sits in a bottle after being cooked down I just don't like the flavor. I add oregano at the very end because I like the aromatic spicyness of it. That all cooks off when reducing the pot for an hour.
Try drier crusts. Instead of a 1:1 ratio of flour to water (by volume), try something closer to 3:1. You might booger it up but just play with it.
Don't think that preshredded cheese isn't the problem because it might be. The whole milk blocks of mozzerella are very moist. If it doesn't feel like taffy don't buy it. You shouldn't have dry little pieces of cheese. This will cause the cheese to harden on the top and it adhere to itself and pull off when you bite into it.