1. The starch comes from the pasta, not the water. Decreasing the water increases the concentration of the starch in said water. That’s why every good recipe for cacio e Pepe I’ve seen recommends using as little water as possible

2. This has been thoroughly debunked. Kenji did a full write up of this but suffice to say that starches absorb water starting at 180 degrees. As long as you have the water above that temp it will cook in the same amount of time.

https://www.seriouseats.com/how-to-cook-pasta-salt-water-boi...