my bike is a heavy "torque monster". Both deceleration and acceleration are mostly controlled by the engine. If I throttle down, the bike slows down a lot. So yeah - engine braking is acceptable.
You'll learn to mix it with some real braking. I always like to maintain a very good feel for both brakes. Here's a simple exercise. Every time you come to a stop sign, or an intersection where you must stop, pick an exact point on the road as your target. Aim to bring your front wheel to exactly that spot when you come to a stop. Then try braking with only the front brake, or only the rear brake, or both brakes together. This gives you a lot of practice in getting a feel for the brakes.
But when I'm slowing down in 3'rd gear and 2'nd gear, most of the braking (if not all of it) is coming from the engine.