I'm going to start by saying that what you're demonstrating here clearly shows a strong understanding of how the things you're drawing exist in three dimensional space, and how they fit together. The tricky thing is, however, that you've pretty significantly deviated from the processes I explain throughout the lesson in a lot of these, which makes the work vastly harder to critique. At least, that's the case with a number of them. Some are more in line with my instruction than others.

It's not that abnormal for students to get to Lesson 5 and to get a little too excited by the fact that they're finally able to draw something they find interesting, and so some will get caught up in drawing animals more from observation than construction, and so they get pretty heavily derailed. This is not the case here, in that the course is focused on developing and demonstrating a strong grasp of 3D space, and you have done that.

That said, there are key parts of the exercise (keep in mind that each drawing is an exercise, where you're being asked to draw them in a particular fashion for specific reasons) that you do end up missing somewhat, so I'll try to address those. In regards to your questions though - for example where you struggle with the sausage method - opting not to use the sausage method really isn't the answer there. Being uncomfortable with a process or a technique is normal - but you don't solve it by trying to change it into an approach that works better for you.

That more or less seems to be the core of your questions - "I decided to do it this way instead, is it bad?" It's not bad, it's just not what you were asked to do here, and it does inherently make my job of critiquing your work more difficult. So keep that in mind.

The first issue I want to talk about is the idea that in our constructional drawings, we try our best not to treat our drawings as though they are just lines on a page. There is a LOT of freedom we get from the fact that we're drawing on a page - this is at least a part of what you describe as being "gestural" - but with that freedom comes the danger that we will make marks that contradict the illusion we're trying to create for the viewer. Basically we can make any mark we wish - but most of those marks will undermine that illusion, rather than reinforce and support it.

So, instead we have to try and think about every step we take with our constructions as though we are working in real 3D space. Drawing a ball for example should be thought of as introducing a solid, three dimensional form into the world in which our object exists. Once it exists, we can't redraw its silhouette - we can only attach new forms to it, or carve into its surface in 3D space. Furthermore, when working with organic subject matter, we have somewhat less ability to cut back into our 3D forms than we would with more geometric/hard surface objects (as explained here) - so looking at how you drew boxes for these dogs' heads resulted in the sense that each dog has a sharp corner sticking out of its form. It is very difficult to ask the viewer to "ignore" the corners of that box, to act like it's not there. And so that is something we should avoid - which is precisely why I push students to construct their heads around a cranial ball.

Over the years of doing critiques I've gradually adjusted and refined how I wish to explain certain concepts, and head construction is something that has definitely evolved. I currently have this explanation in the informal demos page, which you should read in full. I will be incorporating it into the core lesson in the coming months, with dedicated video explanations of the concept, but I haven't yet had time to do that.

What it explains is actually quite relevant to what you mentioned about the fact that you like to "see the planes". Head construction is very much based around the idea of taking these smooth surfaces and breaking them down into a series of distinct planes. The question is, where do we actually separate those planes? By starting with the eye socket as shown here, we're given a starting point from which to start making those separations. You are indeed grasping a good bit of that - your heads are well separated into planes, and they feel very solid and three dimensional. The only problem is that you have this unnecessary box floating outside, and it breaks the illusion you're providing the viewer. Instead of starting with a box and working your way down, starting with the ball allows us to build our way up, adding forms and therefore never asking the viewer to imagine that some form we've drawn is no longer present.

This neatly transitions to the second issue I wanted to call out. Since we are not allowed to simply treat this as a drawing, we must introduce every change to our animal construction by adding another solid, completely enclosed, three dimensional form. This is known as additive construction. Once a form is drawn (and I believe I mentioned this above), we cannot redraw the silhouette of that form to change it. We must build on top of it.

Looking at your work, you tend to be pretty fond of redrawing areas if they don't match what you want from them. For example, if you look at these feet you've got lines sticking out all over, that like the box for the dog's head, you'd ideally want the viewer to ignore. Looking at this leg, I've marked out where you had a "sausage" (it wasn't quite adhering to the characteristics of a simple sausage, but it wasn't too far off), but you then decided it didn't match the shape you wanted, so you just cut back into it and redrew the leg the way you wanted it. When adhering to the rules of how we approach constructional drawing, that simply isn't allowed. Once a form has been defined in the world, you cannot just go in and redefine it. You have to work around it. Sometimes that means accepting that your drawing is not going to perfectly match the reference image, and that's entirely okay. It's more important that your drawing feel structurally sturdy on its own.

Another way in which this can come up is where you're drawing a leg and there's a bit of extra skin/flesh that 'bridges' from the bottom of the thigh to the top of the calf, like in this deer's back leg. You drew that as a simple line, but instead it should have been drawn as a complete form that wraps around the sausage structure. As a side note, you're pretty inconsistent in terms of adhering to certain aspects of the sausage method - for example, you pretty frequently neglect to reinforce the joint between the sausage segments.

The additional masses - like those we add to the structure of the deer's leg - are important concepts that you din't really appear to have made much use of, instead opting to draw simple lines or shapes. The key problem is that you don't end up defining the relationship between these added pieces, and the existing structure.

These pieces we add really need to be respected as separate forms of their own. And so, we can first consider how they exist in the void, before we add them, as balls of soft meat. In this state, they're as simple as possible, consisting only of outward curves. But as we press them against another structure, the part that makes contact takes on inward curves and corners, developing more complexity in response to that contact as demonstrated here. What this means is that in order to attach this form in a believable fashion, we need to also think about how the forms they're touching exist in space.

In essence, there's a lot you're missing out on. Take a look at this quick fox demo. Because you're going off on your own direction, you're skipping over step 2 entirely. Your constructions still feel solid and believable for the most part, but again as I mentioned before - you are in many ways not following the lesson.

Now this critique has gotten very long, so I'm going to stop it here and ask for some pages of revisions. I'm already very happy with your understanding of 3D space, but you need to follow the principles of the lesson itself more closely. This is not just a "how to draw animals" lesson. If it were, you'd pass it easily. It is instead teaching you specific exercises to help develop spatial reasoning skills, and while you've demonstrated that you have those skills, you have not demonstrated an understanding of the exercise itself (or as much of an attempt to follow it as written as you should). You're an excellent artist, but you need to follow instructions more closely, and not deviate from them for your own experimentation here. There is ample time to do that on your own.