Right, I promised you to expand on this so here goes...
First a few definitions:
Volume - the amount of training that you do best measured in hours.
Intensity - how hard you train, best expressed a coefficient of your functional threshold power (FTP), where 1 hour of training at FTP gives you a coefficient of 1.
FTP - The average power (measured watts) that you can produce in one hour of absolutely maximal effort.
Recovery rates - the speed at which organism repairs itself following exercise. There is a mathematical formula that can be used to relate the recovery rate to your FTP, and I am happy to expand on that too, but don't want to lose you right at the beginning
Let's just say for now that the recovery rate has a half-life of around a week, and with small variations that is the same for all humans.
Now if you understand that the training load you can produce per hour is unique to you (pre-determined by your FTP), it becomes clear that your unique ability to dig yourself a training hole will be defined by your fitness. Your actual amount of fatigue is a function of volume and intensity of training that you have done in a week. The amount of recovery that you have had in a week is a function of time. The fitter you are the more you can train, but your recovery rate does not change. There is a formula that gives you a training score based on volume and intensity. An unfit person with FTP of say 200, can reach a training score of 100 in one hour of maximal effort training. The fatigue from that effort will clear away with a half life of about a week. A really fit person with FTP of 400 can reach a training score of 100 in one hour of maximal training. The fatigue from that effort will clear away with a half life of about a week. The really fit person will have won an Olympic time trial with that effort, while the unfit person will have covered 15 miles of undulating terrain, but it will take them both the same amount of time to fully recover. The fitter person will find it easier to dig themselves bigger training holes, and recover effectively - so called functional overreach. But they will not be recovering any faster than the unfit person.
Happy to expand on any points that are not clear.