Most N64 games uses fewer polygons than many PSX and some Saturn games. It's obvious, and can be seen when you use wireframe rendering in emulators.
The difference in the N64 is that it can tile the textures along a polygon, and thus can, as example, use only two triangles to make a gigantic wall, where the Saturn and the PSX would require a quad/two triangles for each tile. Thus why the N64 could push enormous envronments, like PilotWings, the Mario 64 levels and Zelda's Hyrule field.
In Zelda it's quite visible that Hyrule field is made of gigantic polygons that spawns across miles.
On the PSX vs Saturn issue... Burning Ranger's draw distance is bad because the game was overdone, and has awfull culling. It's obivous in many areas that the game is *still* rendering the neighbor rooms, instead of ignoring them. A basic sector-based culling could decrease the poly count by 30% without visual changes.
When you take that in account (the game is rendering rooms you can't see), plus the fact that the game renders a secondary framebuffer for the transparency effects, that the games abuses serious time of the Saturn hardware when the characters take a hit and LOADS of crystals fly all over the scenery, and that some areas have more polygons than needed, I see no problems in the Saturn running MGS, sans some framebuffer effects, of course.
As for VF2 vs Tekken 3... for God's sake! VF2 is a 2nd generation Saturn game, and the Arcade version itself was launched by the time the Saturn was released!
Tekken 3 came to be close to the time VF3 was released. It's no fair to compair the two.
If you want to do comprasions, get DOA at least. The DOA models are up (and sometimes better) than the Tekken 3 models. Plus it runs at a higher resolution, and that's something that has great impact upon the 32-bit systems.