Death Stranding came out in 2019. Death Stranding 2 will come out in 2025. That's six years for two games. If these were the PS2 days Kojima would have cranked out 3 Death Stranding games by now and we'd be getting Death Stranding 3: Subsistence along with a teaser for Death Stranding 4 next year.
Remember when video game trilogies used be to a huge thing in the sixth and seventh generations? You'd typically get 3 games in about 5-7 years
See: Halo, Gears of War, Resistance, Killzone, etc
Okay thanks for clarifying that, iterating is definitely necessary, I didn't think "waterfall" actually meant literally no iteration whatsoever