Well I've never seen this degrading in clones. It's a Fking clone. The only degrading I can see that would happen would be the growers fault by not treating it the same or something happening. Again growers fault.
A mother plant degrading I can see because it's the same damn plant that has gotten older and older and it's worn the fk out.
Think about it: the DNA of the plant can never change, but the environment and health are entirely up to the grower. It’s the old “nature vs. nurture” argument. Healthy plants will give off healthy cuttings, while stressed or diseased plants will give off weak and distressed ones. If something in its environment changes the health of that clone then yes it will suffer and so will a clone you take from it.