The thing is that a force based upon conscription has a better variety to pick from, because it's not only those who volunteer, it's everyone - And it allows it to pick who it needs and where without regard - Of course,
most soldiers (And this has been proven) have been placed where they wanted to be placed, in one of their three top priorities, and this is another advantage the conscription force has - No lack of men.
If you're not stressing over how many people you can assign to where, and if you actually have extra people to assign wherever they want, it means that most people will get what they want.
I'll explain better:
Let's say soldiers 1 - 20 have selected "Tank Commander" as their top priority.
Soldiers 21 - 40 have selected "Ship Commander" as their top priority.
And soldiers 41 - 60 have selected "Military Engineer" as their top priority.
And in all those roles, you need to fill in only 20. This means that all of those soldiers will get what they want, and you can continue to do this with others and their second and third priority, making sure that almost everyone is happy.
Now, with the excess of men like this, you also make sure that you pick the absolute
best for the jobs you need them, meaning the best equipped, best tooled and best skilled for the job, not just those who volunteer.
This is what an all volunteer force lacks, the two examples you showed didn't get what they wanted - And that's because of lack of man power to assign you to the places you want. They have had to assign you elsewhere to fit their needs, but in conscription, when many pick different priorities, the military can quite easily please everyone.
Don't you think that a volunteer soldier that did not get what he wanted would be quite a bit more discouraged than a conscripted soldier that did? Despite what I already said earlier, that morale rarely matters outside training - You seem to like the subject, so I ask you, don't you think that a volunteer soldier that did not get what he wanted would be more discouraged than a conscripted one that did?