Flour for sauce: In the broth or in the oil?
If you add the flour to the broth you don't have an opportunity to cook the flour separately. 

Roux is described by its color. Even the lightest whites or blonds are cooked a bit to remove some of the raw "cereal-y" flavor of the flour. Toasting it just a little removes this and it's generally considered an unpleasant taste. 

Darker preparations bring out a nutty quality that is sought after for dishes like gumbo.

You're basically making a slurry, which is a normal thickening technique (you mentioned the other two). Generally the starch is mixed with a small amount of cold liquid and then added to the sauce to thicken

If you don't notice the raw flour flavor in your sauces, I'd say your technique is a fine solution. Probably due to the relative amount of flour you are using. You may notice it's not ideal for a thicker sauce.