I think without Sony, Sega would have won. Consider:
Dreamcast came out mere 2 years after the N64, and was a world of difference in terms of experience. N64 games were low poly, blurry, low fps mess. Dreamcast games were rich, fluid, crisp, just next gen. Compared to Dreamcast, N64 games looked really fucking grim.
The gap from Dreamcast to GameCube in 2001 would be a further 3 years. During this time developers would either be stuck with cartridges, or defect to Dreamcast to make cheaper, bigger, more impressive games. That would have boosted the entire platform.