Uh no. SHIV is built on the same engine as SHIII, with obvious graphical and feature improvements. If anything, stock SHIV, especially with the U-boat add-on, is leaps and bounds better than stock SHIII, both graphically and in terms of realism. It's only with mods that their 2-year age difference gives SHIII more claim to refinement.
If you were to get only one game today, I would suggest SHIV over everything. It's great and will get better. It's the subsim of today and tomorrow. But SHIII with mods like GWX 2.1 and SHIII Commander is an experience that I think no subsimmer should miss either
