terminal velocity has everything to do with mass!
read carefully:
More massive objects will only fall faster if there is an appreciable amount of air resistance present.
an aircraft with a 5 sq ft plate area travelling at 400 mph at 10,000 ft will have 1,500 lbs of drag, you can't ignore air resistance.
Now consider two aircraft, one 12,000 lbs and one 6,000 lbs. As f=ma, or f/m = a, where force = weight - drag, we get (w-d)/(w*32.2)=a, now at 1,500 lbs drag at 10,000 ft, we get an acceleration of 28 ft/sec^2 for the 12,000 lb aircraft and 24 ft/sec^2 for the 6,000 lb aircraft. After 10 seconds under the same conditions, the 12,000 lb aircraft will be travelling at least 27mph faster.
At terminal velocity, where weight = drag, the 12,000 lb aircraft will "theoretically" ignoring prop drag and (mach) compression effects based of a 5 sq ft plate area, will have a terminal velocity of 1130 mph at 10kft, the 6,000 lb aircraft will have a 800 mph terminal velocity.