For many it is the best NLE that ever existed. For years it lead the way with innovative features, and arguably it could even have influenced the design of FCP X with its elimination of the source/record style interface. It is of course Vegas Pro. Michael Bryant takes us through the origins of this unique, and popular software.

https://www.redsharknews.com/production/item/4935-how-vegas-pro-rocked-the-nle-world

I suspect you could work without a source viewer on NLEs before Vegas. a demo video for the AVID One in 1989 shows the editor bypassing the source viewer and directly placing the clip into the edit. Vegas has the trimmer which more or less works the much the same as a source viewer. I know that you can use Lightworks without using the source viewer, working directly with the clips in the bins much the same as FCPX.

FCPX seems to have picked ideas from various NLEs.