Small hills, maybe, anything larger and longer than a good-sized roller is going to require you to climb it at a slower cadence. The strength comes from being able to keep turning the pedals at slower, much harder rates for longer periods of time. Prolonged 6%-7%+ requires a different type of strength than the short bursts up smaller gradients.

A reasonable cadence (based on power output) up a shortish (@1 miles) 6% hill would be 40-50rpm which is around 8 miles an hour at 70 inches fixed. The strength required to achieve this goal is different than being able to sprint/spin up shorter/less steep hills.