Before I get into details on the question I want to preface this by saying that I watch a ton of video tutorials, do a lot of imaginative drawings, read about and drawn a lot of figure drawings, and gathered a huge library of reference and inspirational images.

Now while the above is all true, up until now I've mostly been operating on muscle memory (basically drawing by trial and error). Whenever I attempt to create a character, I can execute a pose with simple gestures but when it comes to constructing anatomy I never know what reference to pull out, so I mostly focus on trying to remember how the muscles and bones move. After I get a base down, I have trouble designing outfits and looking for reference and tutorials on how to do so.
When I attempt to create an environment I usually start with a perspective line and draw in small gestures for buildings and mountains, but when it comes to outlining the scene, I lack any visual knowledge of architecture so it ends up looking like generic cubes and cylinders with random roofs.
In the technical aspect of drawing, I feel like I have a good understanding of value, shading, and line work. Color I'm still trying to study and perspective I feel is my greatest weakness. Now when it comes to design, I feel as though my visual library is lacking and no matter what I watch, read, observe, or attempt to make from a study, I'm not learning much (hence the reason why I operate on muscle memory). In video tutorials like Feng Zhu, his information gives me a great understanding of the things I'm trying to learn mostly because he uses science to teach it; but he purposely doesn't give an explicit explanation of the fundamentals since most of that is taught with his students.

So basically I think I'm either muddled with too much information to know where to start or too lazy to find out where to start if that makes any sense. I want to avoid being complacent with my work and start improving so that I can build my portfolio to a professional level. Now should I be working more on learning and understanding the fundamentals (science and techniques) or building up a visual library to help improve my designs? Also what are some good exercises/advice to help learn both? I'll link to some of my pictures to help understand where I'm coming from.

For a background of myself, I'm in art college right now studying animation and game design though I'm focused on learning digital painting, concept art, storyboarding, and 3D modeling. I had a previous interest/background in comic art so some of my older work may reflect that.