When first starting out, I found, by trial & error & forums, diet (low carb) was critical and brisk, regular walking helped tremendously. At the time I weighted the importance of diet as 70%, exercise 20%, sleep and stress reduction 10%. ALL these work together to get BS down so none should be neglected.
Aerobic exercise (walking) allows the body to use oxygen to burn glucose 19X more efficiently than anaerobic (spints, HIIT, weight lifting) exercise. For me, walking does work wonders after a meal to burn glucose in muscles and make more room for the newly digested glucose in the blood stream. Walking only goes so far because the room to store glucose is limited in a T2D.
Recently my interest has turned to "How can I increase my insulin sensitivity"? To do this means increasing the glycogen storage capacity of my muscles to give BS someplace to go. If my muscles could store more then my BS wouldn't go so high. And I could clear the BS using less insulin too. Incredibly, anaerobic exercise (sarcoplasmic hypertrophy) causes muscle cells to create more glycogen core molecules, increases the cell size by increasing cytoplasm and increases the number and volume of other enzymes. This muscle adaptation effectively reduces insulin resistance and consequently reduces A1C. It also means I don't have to take 3X daily walks to burn off glucose.
Now, I'm inclined to believe the importance of diet is more like 40% and exercise 40%.