You have a lot of enthusiasm and ideas, and it needs to be channeled in a usable way. Every time someone gives you feedback you find a reason to ignore it or say “I don’t know the technical aspects”. In the professional world you will need to listen to feedback, take it in, think about it and integrate it. Start demonstrating how you can apply the information being given back to you.
Forget the renderings for awhile. Get the design right. Once the design is correct, then begin a rendering.
Check out the below image. I put some magenta lines on your last sketch to show where to push the proportions to get that right first.
Also, the second image shows some basic foot terms. You can learn a lot more about the anatomy of the foot simply by googling.
It helps to start by sketching feet. Stop thinking of them as shoes, and start thinking of them as prosthetic calluses with cushioning. When I started designing footwear, I started by drawing feet, then adding layers. Cut up a bunch of old shoes with a hacksaw and an exacto knife so you can see what goes inside.
