Whilst I agree with the sentiment all that tells you is that at a net level over the 20 miles your two lanes moved a similar speed (which isn't surprising). As you correctly identify the 'weavers' will chase the moving lane, and will thus potentially benefit whilst the lane you were in, or that which the lorry was in, are stationary.
What really annoys me is our insistence on queuing. If there's a 2 lane road merging into 1 lane we all insist on making sure we're in the continuing lane a mile out, and identify that it's a certain type of driver who goes screaming up the now empty lane to the point of the merge. However, by far the most efficient way to deal with this is to merge in turn, like a zip, at the point of merging, not create a wholly unnecessary queue before that point. I will always join that queue though, as you get a few heroes who think they're being awesome by stopping anyone merging at the point a lane closes, and are thus perpetuating the problem for everyone. I don't really get how so many people can have such a fundamental misunderstanding of how it should work. Seems to be an innate knowledge among British drivers. Rage.