Hi CaesarAnto, thanks for your email. I'd like to add some initial comments on your observations.
I think I would change the mindset from a right side (foot) that is doing too much work. Essentially the foot is the platform that the body 'lands' on as we take a step. It is a load absorber, using the mechanics within the mid-foot (arches) ankle, knees, hips etc to absorb the transfer of the weight in a smooth manner and then prepare the body for that transfer to the left side as the toes come off. So it is possible that is any part of that mechanism is not working as it should then the load will have to be shared/absorbed more in the other areas/joints. That can lead to them taken on more than they can, or wish to handle which can then lead to injury or discomfort (which then essentially is the brain telling you that those areas are not exactly happy with the situation).
The first thing to do is assess the right sided joints from pelvis to foot to see if they have normal movement. Perhaps they never have which lead to the initial injury of the right side? It is common to have torsions in the legs (rotational twisting of the bones) that can be asymmetrical which can lead to progressive issues. If the right side looks normal it could then be that an issue on the left side, such as reduced hip rotation at the left leg, which leads to the right leg landing more on the outside of the foot. That will wear out the outer side of the soles of your shoe more quickly than the inside. Now landing in this way (supinated) will lead to excessive pronation then as you transfer the weight to that foot. I am sure this reads in a rather complicated way but with your therapist they should be able to explain this in simple terms.
My advise would be to have a gait assessment. To really look at how you are moving from leg to leg and then combine that observation with the physical assessment. It is likely that some form of orthotic or a change in your trainers will be of some assistance and that your initial experience with that was just not the right orthotic selection (It can be very specific).
Lastly at 6'4" and only 75kgs it seems like you are a tall and slim in stature. This makes for long levers in the body which can predispose your to these sorts of issues. It is all very normal and you are doing the right thing in wanting to have a little more understanding about the issues and find the best way to manage them going forward.
regards
PB