at BEST Lanfear was half as strong as Alivia ... likely much more over matched. That would be like a child fighting an adult.

It's clear that you can slice the flows of even a significantly stronger opponent (we see Cyndane do it), and splitting flows has been shown to be a matter of skill not strength, which adds up to skill eventually prevailing over strength in most duels. Unless of course the stronger Channeler gets lucky or is skilled enough to wear down the weaker.