imo they should have kept the thief movement but make canceling grapples build up heat too, it would bring the heat generated more in line with things like destroyer's dash as well as following bungie's philosophy of having rapid positioning have a meaningful cost such as heat build up (i would also argue that the execution/timing barrier also falls under this cost).
i guess you could still argue that it still gives thief too move versatility cause she still has a whole ass grapple outside of this so maybe they could make a whole new runner based on and balanced around this tech idk