IMHO, lob serves are not defensive, because if done correctly, they put you in an offensive center court position and your opponent deep in a back corner.
Most beginners have trouble controlling lob serves because they put too much energy into the ball by using a forehand swing. However, the lob requires a new stroke technique. The lob stroke has the fewest moving parts. To gain control, you need to lock both your wrist and your arm. They remain locked throughout the lob motion. Use your shoulders to move your arm and racquet.
Plus, you do not need to put much energy into the ball, so use a very short backswing. The lob stroke should feel more like a push. So push the ball to a target point on the front wall.