Too much light is rarely a problem! You are correct, aperture controls how much light gets through the lens to the sensor (or film). There are actually three components that make up exposure: Aperture, Shutter Speed and ISO. If you're in low light, you need fast lenses - that's just how it is. Turning up the ISO can fix one problem and cause others, but nothing beats lens speed (like 2.8 is faster than 5.6, etc).

Also, from your previous posts, I think a consumer variable aperture lens is a step in the wrong direction. It's pretty rare to find a consumer lens made out of metal. They can be pretty sharp stopped down one or two stops from wide open but pro lenses are designed to be sharp wide open - which is already faster than the consumer lens. For example, the 80-200 f2.8 is shot wide open (I have the two-touch Nikon previously discussed and can tell you from experience it's sharp wide open). Say the consumer zoom is f5.6 at the 200mm end of the zoom range. Stop down even one stop (f8) and you've lost three stops over the pro lens. You've lost two stops even wide open and the image might not be sharp enough for you.

A fixed aperture lens is generally higher quality than a constant aperture lens, but not because of that reason. Constant aperture lenses are bigger, heavier and more expensive. Variable aperture lenses are built to be light weight and inexpensive. Nothing wrong with variable aperture lenses, I'd rather carry a 1lb lens than a 3lb lens but just realize that there are tradeoffs.