Humans are evolutionarily predisposed to have endurance. AS a species we are some of the best endowed mammals endurance-wise. On the other hand we pretty puny when it comes to speed and power. Track coaches have a saying: Sprinters are born, distance runners are made. Mean that you can take almost anyone and turn them into an endurance athlete but speed and power athletes come out of the box with a really special set of genes.
So unless you are way out on the tail end of the endurance bell curve I suspect there is good hope that you can over come your ADS given enough time. From the endurance athlete perspective you have really messed up your metabolism with the steady diet of high intensity work. That’s why you suffer so badly on long outings.
Follow the precepts on the book and on this website. It is going to take a long time: Months to see significant change and years to reach your genetic potential. No one can tell you how fast you will adapt because trainability does have a strong genetic component.
The good news is that we have worked with a lot of reformed Cross Fitters and they usually have a very high general work capacity. They can handle anything we throw at them. This is a valuable asset and if you have time tom you can speed up the aerobic adaptation process by doing more volume of low intensity aerobic training. Duration is the biggest stimulus to aerobic adaptation. 10 hours a week is going to give you twice the benefits that 5 hours will.
Fixing ADS is a slow process and you’ll probable need to go a painfully slow pace. Do it and you will see results. Be patient.
Scott