Hopefully this analogy will help, as will reading the Wiki link on what adaptogenic herbs do.
Tires on a car = CNS, adrenals
Alignment (of tires) = training
If the alignment is such that the tires are wearing down excessively quickly in an abnormal pattern, then there is a problem. The cause is the misalignment. The wear pattern on the tires is a symptom.
By re-treading the same tires (using adaptogens, for example), we can reduce the symptom. However, this only means that we have given ourselves more time until the tires wear down in the same pattern as before, as the cause has not been addressed. One benefit to things like adaptogens is that their effects on the symptoms are often felt very quickly, which is good for the mental state (however, not so good if the person keeps doing what burned them out in the first place!)
Only by addressing the faulty alignment can we fix the cause. Adaptogens are not treating the cause, they only treat a symptom. In a "healthy" person, adaptogens help them to perform better than they might normally. In an "overtrained" person, adaptogens are only helping them to dig themselves a deeper hole. The deeper issues of what is hindering recovery is the cause(s) in this case.
Caffeine is a stimulant. To rely on a stimulant to fix dragging performance levels is like beating a dead horse. It only makes the problem worse.