Tamron 18-270 vs Nikon 70-200

I just tried a little experiment using a Tamon 18-270 with Vibration Control vs a Nikon 70-200 without Image Stabilization.

Both lens were at 200mm. The camera was at ISO 1600. The difference was in the
f stops and shutter speeds.

The Tamron was at f5.6 handheld at 1/15 of a second (with VC).

The Nikon was at f2.8 handheld at 1/60 of a second (No IS).

Essentially the same exposure. (2 stops either way). The point of the 'experiment' was to see if I could handhold the Tamron at 200mm with VC and get a sharp image properly exposed at 1/15th at f5.6 (in low light) vs the benefits of a fast lens like the Nikon 70-200 at 1/60th at f2.8. Remember both exposures are essentially the same.

Both results were acceptably sharp and properly exposed.

So my question is: What is the point of spending over 2 grand for a 70-200 f2.8 lens when the vibration control available in todays lenses allow you to gain 2-3 stops in shutter speed, thereby allowing the use of 'slower' lenses with an f stop range of f3.5-5.6.

Marvin