1.2.- Why HFS suspension is more progressive than a traditional one?

Because deflection is combination of a gas spring together with an helicoidal one (both put in serial).
Gas has a progressive behaviour by nature.
In HFS system, the spring rate and recommended pressure setting is adjusted for each individual motorbike, seeking for having a first half of fork travel working mainly with gas spring, and the rest of stroke mainly with the helicoidal one (progressively along all fork travel!).
Adjust is recommended to have more bottom resistance.