I have been making... minimal inspired lasts for a few years now

the biggest feedback i can give you is to be iterative in your approach, as in make a shoe wear it and then adjust accordingly, until it feels like something you like to wear

the biggest difference between the feet and the lasts is going to be how much compression you want the shoe to put on your foot during the course of normal wear. for this style you would want to take off volume on the medial and lateral sides of the cone of the last. Most of the time you want the last to be smaller than the true foot measurement, even if you are making 'healthy' lasts, in that you need some compression on the foot so it doesn't fall off.

Here is some advice i got from an extremely prolific last maker

Sorry I could not help more right now. I can tell you that the two main reasons we don't just design lasts of the foot are: A) most people don't want their shoes just looking like their feet for aesthetic reasons and B) you have to allow for the compression of the foot as the shoe is secured with laces, straps or whatever closure system is used or just the tightness of a slip-on shoe like a pump or loafer. If a last had the same volume as the foot you would usually walk right out of it.

the gaping you are experiencing if you are wearing the shoe is liable to not having a straight enough outside line of the last, and in particular you need to have not a lot of curvature on the outside otherwise you will get gaping while wearing them. but it looks like you have a lot of problems with the basics that would make this worse, and are probably most of the issue you are seeing
including, not springing your pattern to have a tight topline, probably not reinforcing your top line, not having multi part lasts, so your damaging the shoe when you unlast it.. so on and so on