Sure.
It speeds up recharge. That's it. It doesn't speed up activation time, animation time, damage dealt or anything else. If your highest dps attack chain already has no gaps in it, there would be no change to that attack chain's dps.
If using hasten allowed you to use a different attack chain that does more damage, it might be 70%. It could also be 15%. It might be 127% more damage per second.
A 70% increase in recharge does not translate directly into 70% more DPS, because recharge isn't the only variable. Activation time, animation time, damage, accuracy, target caps... heck if you wanted to be pedantic even movement speeds impact your DPS. Different powersets and different builds will take advantage of recharge at a different rate.
Faster recharge could mean more damage. Maybe it means a lot more. Maybe it means a little bit. Maybe it means no more damage. It varies widely based on so many other factors.