They look in need of a good trim. They look like they could be very nice feet with a few good trims and some healthy, well attached growth. That right fore especially looks like it has a very long toe. It will be interesting to see them after they've been trimmed. Clean feet & some different angles - check out my signature link - would be helpful too.
I think diet & nutrition is a big cause of the cracks & it will take some time for all the 'micro cracks' to grow out. The bigger ones will need to be dealt with, with trimming & treatment too, but sounds like the farrier was doing that. I'd be opening up those seedy looking cracks as much as necessary. As there is little integrity there at the moment anyway, I don't believe it would further reduce it, and I it's necessary to treat infection along with mechanics & diet in order to grow strong wall.
As the weak walls have little integrity around the bottom half at least, as is seen by the flaring, I'd also be inclined to unload them. *It would also depend on environment & degree of flaring & such as to specifics. I have found this sort of approach allows the foot to become stronger in the long run and the walls will then be capable of sharing the load.
I put some hoof treatment on them almost everyday. It has been extremely muddy here lately and is just drying out so I am trying to keep her feet from getting to dry.
It's the mud, not the dry that's a problem. Horses, hooves & all, are built for a semi arid environment & hooves are meant to be dry. I wouldn't put anything on them, aside from treating for thrush & perhaps strong saline soaks to dry them out too, if the environment's eternally muddy. Hoof 'conditioners' & other topicals can make their feet look prettier, but they do very little if anything for the health of the feet. If they're oil based or such & there is already seedy infection, it'll only provide the bugs with a nicer environment too. Check out this report; High Performance Hoof Care - Hoof Dressings
We have selectively bred horses for thousands of years, often with out thought of their feet. Not all horses have "mustang feet" that can with stand work with out shoes.
Sure, genetics do come into it - there are some badly bred lines with terrible feet for eg, but I don't buy the 'bred the feet off 'em' argument to a big degree. I don't think it's so much about 'nature', but I do think we've 'nurtured' their feet away. IOW it's how they live, eat, are treated. This is often changeable though, so we can potentially develop our 'mustang feet' But at the end of the day, it comes down to the same result, that many domestic horses require hoof protection to do what we ask of them. I think hoof boots are a great alternative to steel rims.