If the fan motor is turning, the blades are turning. It may be that the booster is working against pressure, and is not able to reach a rate of airflow that you can feel. Additionally, the lint screen box may be leaky.
Regarding tight homes needing air exchanges, that is definitely true. But it is ideal to control the rate of those changes, and to filter and condition the outside air as it enters the house. An HRV in a tightly sealed house allows that. The humid air entering from outside will still be dried out by your AC system before it goes to the dryer, so, one way or another, changing the RH of that air to absorb moisture from the clothing is accomplished.