>>11198555"heavier versions of an electron" is totally a reasonable way to think about muons and taus. that doesn't mean they aren't as fundamental as electrons though. they aren't made of electrons, and e.g. their masses don't follow from the theory, so they have their own special features that make them distinct from electrons.
for sure they aren't "heavier states of an electron" though, because then you would expect that they could decay into an electron without emitting some particle that carries away their muon or tau number. what i mean by this is that there are processes like mu- -> e- + nu_mu + anti-nu_e, which conserves the muon number. however if it were just an excited state of the electron then you could write mu as e* and you would expect processes like
e* -> e+gamma
or
e* -> e+higgs
but since that is kinematically not allowed for an e* with the mass of a mu, you would expect something more like
e* -> e + gamma + gamma
through a higgs loop or some other spin-0 loop
