Yoga asana practice can be, but doesn’t have to be exercise. My experience is that Ashtanga Yoga is good for building strength, increasing flexibility, and providing a cardiovascular challenge but it is better at working with the nervous system and preparing the body for meditation.
The more experience one gains, one does not try to move through the practice more quickly, or with fewer breaths, or with increasing repetitions of a movement or posture. The practice is what it is and we are to observe how we relate to it. Drills are better suited for times outside the formal practice. Separating drills from practice is a good way to work on non-attachment.
I approach my practice more like a dance than a workout and that has brought about a certain freedom.
Obviously time and space place limits on our physical practices. Let Yoga do what it does best then go for a walk, a ride, or lift some weights.