I see where you come from. But imo you should work on that guard I think this is the main reason you do not do well against higher level fighters. It is hard to study defence and practice it. What worked for me after you noticed my stance is go for private boxing lessons where I learned a lot regarding stance and guarding. Have you got some legit boxing coach to try to talk to for some lessons on the basics? If I were you I would drop the striking classes for a bit. While they are fun and filled with spars and partnered drills which are essential I d say drop them for the sake of the health and focus purely on technique and practicing on the pads and the bag.