Several dictionaries (eg, Collins, MacMillan, Cambridge) essentially agree with the definition of quintessential mentioned in the question. Thus quintessential example is effectively equal to most exemplary example, which from a pedantic point of view is a bit redundant. However, aside from those pedants who recoil in horror from quintessential example as a monstrosity, most English speakers will have no trouble understanding what is meant.
As suggested in akberc's answer, it is slightly perverse to refer to the electron as the quintessential apparently-elementary particle, when most of the
31 elementary particles are representative only of themselves, rather than being representative of elementary particles in general. But that is a semantic-content issue, rather than an English-language question. From a language point of view, your alternative wording is better than the first. However, the parentheses around apparently are a noisome distraction and should be dropped. Or in some other sentence explain that wherever you write elementary you actually mean apparently-elementary, or elementary according to theory X, etc.