  We study the spin-1 pyrochlore material NaCaNi$_2$F$_7$ with a combination of
molecular dynamics simulations, stochastic dynamical theory and linear spin
wave theory. The dynamical structure factor from inelastic neutron scattering
is well described with a near-ideal Heisenberg Hamiltonian incorporating small
anisotropic terms {and weak second-neighbor interactions}. We find that all
three approaches reproduce remarkably well the momentum dependence of the
scattering intensity as well as its energy dependence with the exception of the
lowest energies. These results are notable in that (i) the data show a complete
lack of sharp quasiparticle excitations in momentum space over much, if not
all, of the energy range; (ii) linear spin-wave theory appears to apply in a
regime where it would be expected to fail for a number of reasons. We elucidate
what underpins these surprises, and note that basic questions about the nature
of quantum spin liquidity in such systems pose themselves as a result.
