Inelastic scattering cross sections to individual bound excited states of Sn-104 were measured at 150 MeV/u beam energy and analyzed to evaluate the contribution of neutron and proton collectivity. State-of-the-art Quasi-Particle Random Phase Approximation (QRPA) with the D1M Gogny interaction reproduces the experimental proton collectivity and our inelastic scattering cross sections once used as input for a reaction calculation together with the Jeukenne-Lejeune-Mahaux (JLM) potentials. Experimental inelastic scattering cross section decreases by 40(24)% from Sn-112 to Sn-104. The present work shows that (i) proton and neutron collectivities are proportional over a large range of tin isotopes (including Sn-104), as is typical for isoscalar excitations, and (ii) the neutron collectivity dominates. It suggests that the plateau in the mass range A = 106-112 displayed by E2 transition probabilities is driven by neutron collectivity.