Thank you @barnesthenoble and @SashaBast for the podiatrist recommendations. I may end up going that route. I had the horse up to UC Davis for the MRIs so that would be a natural choice. I have done the diagnostics and he is getting other appropriate support. Something needs to change with this horse and maybe glue-on work is the answer.
Boot fit is absolutely critical for ridden work, but I have done speed work and jumped in boots, as have many other people I know. Until you get the shoe situation sorted, I would look at some other boot options as they all have a different fit (the cavallos tend to be more round). I like the easy care line, but the renegades also are cool. https://renegadehoofboots.com/
There’s a breeder in NorCal that exclusively uses scoot boots for her warmblood horses when they work as they are all barefoot.
A well fitting boot is a great tool to have so that your horse can continue working when he throws a shoe, or if you ever want to give him a break from shoes (say, over winter, when it’s soft and he’s pulling shoes weekly - ask me how I know ).
Good luck!
That is a remarkable thing to think.