Heavy weather sailing
Here''s the point, in heavy air, you want to be blading out your mainsail, in other words, making it as flat as possible and then reducing its angle of attack. This reduces weather helm and reduces heel. To do this requires tensioning all of the controls on the mainsail (outhaul, halyard, vang, and mainsheet, and backstay- if you have an adjustble backstay) and dropping the traveler to leeward.
When you ease the vang and tension the topping lift, as you had originally suggested you are powering up the sail and twisting the sail, which increases weather helm and heeling, and reduces drive. Since this is a forum titled "Learning to Sail", I think that it was important to explain that your advice was not the best solution in heavy conditions.
If you took my comments as a personal attack, I am truly sorry. My comments were not meant as one.