Flow rate does not really increase capacity, just the rate at...

Flow rate does not really increase capacity, just the rate at which it disappears. Think of it this way, you have a container with 10L capacity with 2cm Diameter opening. Now you increase the opening so more water can flow out faster (data speed), did the container size (capacity) change? Absolutely not! But you can make a bigger container! (charge more money) the capacity is already there.

Now if you are offering a higher data limit with higher speed, sure you can do that but the data is going to cost more and hence price is going to go up, so unfortunately you can't just get more free data, except with Overpass!!!