  The description of final-state interactions (FSI) in the large phase space
probed in neutrino experiments poses a great challenge. In neutrino
experiments, which operate under semi-inclusive conditions, cascade models are
commonly used for this task, while under exclusive conditions FSI can be
treated with relativistic optical potentials (ROP). We formulate conditions
under which the ROP approach and cascade model can be directly compared. We
feed the NEUT cascade with events from a relativistic distorted-wave impulse
approximation calculation that uses the real part of an optical potential. Cuts
on the missing energy of the resulting events are applied to define a set of
events that can be directly compared to RDWIA calculations with the full
optical potential. The NEUT cascade and ROP agree for proton kinetic energies
$T_p > 150$ MeV for carbon, oxygen and calcium nuclei when a realistic nuclear
density is used to introduce events in the cascade. For $T_p < 100$ MeV the ROP
and NEUT cross sections differ in shape and differences in magnitude are larger
than 50 \%. Single transverse variables allow to distinguish different
approaches to FSI, but due to a large non-QE contribution the comparison to T2K
data does not give an unambiguous view of FSI. We discuss electron scattering
and argue that with a cut in missing energy FSI can be studied with minimal
confounding factors in e.g. $e4\nu$. The agreement of the ROP and NEUT for T2K
conditions lends confidence to these models as a tool in oscillation analyses
for sufficiently large nucleon kinetic energies. These results urge for caution
when a cascade model is applied for small nucleon energies. The assessment of
model assumptions relevant to this region are strongly encouraged. This paper
provides novel constraints on cascade models from proton-nucleus scattering
that can be easily applied to other neutrino event generators.
