I think the skeleton has importance for proportions, while muscles are important for the eventual lines/curves
Just my take on it, I'm not an expert on this, still learning and have my problems with this subject myself
Sorry for the long read, became 3-4 times as long as I expected
Also sorry if it's written kind of awkward. I tend to get lost in typing what's in my thoughts. (You might just need to put your own thoughts on some thing to get it)
Was a quick type, Tried dividing it into subtitles for better read
--- My school experience with anatomy for Skull
Here one semester takes about 7 weeks on my school (? US to Dutch education translation can be confusing)
We had one semester with Anatomy, though just the skull. Eventually we just didn't have enough time for the skull, let alone the entire skeleton And muscles
But the big focus and purpose of the lessons were the proportions of the skull, after that we applied the muscles with transparent paper
This to get an understanding how the muscles cover the bone and tell us how the face becomes what we see for real with skin and all, because that is Very different from the skull
Because of the skin we can have a hard time at guessing the proportions of the face because it's not something we "look" at
But in every face, that skull is indeed there. And it's important
--- My take on purpose of Skeleton and Muscles
Now while we haven't done a complete skeleton, I think the same applies to that, but with added aspects like motion
The "stick" figures some people use to set up a pose usually seem to represent the skeleton.
Because the skeleton is that what has the joints and all. Those pivot points are very useful to get the muscles right and of course the proportions
But when it comes to muscles, those make up allot of the final shapes and curves that are seen by us.
I find it important to have them applied at roughly the right location on your "skeleton".
You will need to know where what muscle is, comes from and goes to, how it changes shapes with different gestures.
With the help of the proportions in your skeleton, the appliance of muscles should go fine and look correct
My conclusion to this would be that the Skeleton is very important to get every proportion correct and very important as a guideline for the muscles and everything else.
Bones don't change shapes, Muscles do, so it's much easier to "calculate" with bones
--- Some further afterthought ...rant? Some about my take on teaching it
Not saying that a skeleton is a must, but it can be helpful
And it doesn't hurt to just skip the skeleton and go straight to muscles. Seen enough people from all camps making different approaches.
Also seen people who do seem to have that skeleton in the back of their head, but don't have to put it on paper or anything
When something is wrong in proportions one can fall back to the skeleton for help, if the curves of the body are wrong muscle wise, one can fall back to muscles, etc.
But both are part of the body
As always, it's easy to say that us humans are different in so many ways, it's hard to design lessons that fit everyone.
Better yet, I would say it's impossible to give everyone the same attention/feedback/help. But I can understand it's very hard to tutor every student separate
It's best to look at each class and see what the most common "mistakes" are and focus on that when teaching. And on the Skeleton <> Muscle topic, I think it's useful to know where they shine the most,
and if possible have a muscle first approach for those who can use it and same for skeleton
But I'm not expert on teaching either, so can't really go into that