Then compare the drain from one F10 Manabolt spell getting a single net hit for 11 damage to a F5 Manabolt spell with 5 net hits for 10 damage.
Because I feel like doing this math instead of cleaning my kitchen:
Normal Rules: Force 10 Manabolt = 5 drain; Force 5 Manabolt = 2 drain. Doubling force more than doubles the drain.
Optional net hits used drain rules: Force 10 manabolt with 1 net hit = 6 drain, Force 5 manabolt with 5 net hits = 7 drain. Doubling force reduces the drain by 1.
Using Fireball as an example:
Normal: Force 10 = 10 drain; Force 5 = 7 drain. It's not a doubling of drain, but it is a noticeable increase for casting a more powerful spell.
Hit-based: Force 10, 1 hit = 11 drain; Force 5, 5 hits = 12 drain. Again, doubling the force of the spell ends up reducing the drain.
And in both cases the lesser drain is coupled with a 1 box of damage higher result - which is important when dealing with 11 box condition monitors.