Never used cornstarch for sauces - but then gravy and pickled beet sauce are the only two I make. I really am not a good cook except for the things I know work well.....
I make a ton of gravy when I slow cook a beef roast. ...using just a package of Onion soup mix for seasoning. Delicious for seasoning. ....Then I freeze the gravy, even with a few beef bites Makes for great hot roast beef sandwiches later, or Rice and gravy meal.
My grandmother used to make her meatloaf with the Lipton’s Onion Soup. I still like it better than made any other way.