Even if not speaking about Karpov's many times stronger mental and emotional stability, it is enough to see where Karpov participated in the period 1969-1975, and what is more important - his results in that period, to see if Karpov's chances were "zilch" or "not zilch". Bobby did have to be worried of that
Karpov's mental and emotional stability is one big unknown. He suffered several failures due to "bad nerves" later in his long matches vs Kasparov and he tended to lose weight, probably due to digestive problems causing loss of apetite under tension. I used to think he suffered with proper mental anorexia (and prof. Zukhar was his therapist), but I find it implausible now.
Fischer's play was sound, stable and consistent.
We are speaking about 1975, your sarcasm is really irrelevant.