The tutorial doesn't explain that you can in fact lock on to enemies outside the blocking stance.

At first I thought the blocking stance was already the lock on system, but then I got annoyed that I couldn't switch between enemies. That was until I used the right stick button and noticed it does change the enemy you're locked on too. But then my annoyance became another one, there is no visual cue to which enemy you are targeting.
It was only on my second playthrough that I found out pressing the right stick button outside the block stance is the actual lock on system with a visual cue and you can also change target by just moving the same stick, or by pressing it if you are in block stance.