You're kind of asking, what's better in a car, the engine or the tires? Can you go anywhere if either one is malfunctioning??
BOTH components contribute. If the preamplifier is slow, the amp cannot recreate information it is not receiving. It's a team effort. And, in fact, if your amp and preamp are fast and the speakers are slow, it won't matter that the other two have fast rise/settling times. You still will not hear the decay of overtones into the recording environment that "fast" implies. ALL the components must be equally matched. Whichever component is the "weak link" in one's system is the one that will destroy the illusion of presence or immediacy.
BOTH components contribute. If the preamplifier is slow, the amp cannot recreate information it is not receiving. It's a team effort. And, in fact, if your amp and preamp are fast and the speakers are slow, it won't matter that the other two have fast rise/settling times. You still will not hear the decay of overtones into the recording environment that "fast" implies. ALL the components must be equally matched. Whichever component is the "weak link" in one's system is the one that will destroy the illusion of presence or immediacy.