Star Trek vs. Star Wars (and a collection of memes)

First, we're comparing a lightsaber against a chainsword, not a Jedi/Sith to a Space Marine. Imagine a human with a lightsaber against a human with a chainsword.

Second, while the 40k universe is a more dangerous place than the Star Wars universe, a Sith stomps a Space Marine. For a Space Marine to have a chance, he must be a psyker (then we have contest). An "ordinary" Space Marine would be cannon fodder; force abilities are a game winner. Most Space Marines are not psykers, so your point on their large numbers is moot.

Third, that video depicts one person's artistic view on how the battle would go down. In no way definitive... and even in the video, Vader could have easily swept the lightsaber blade up when he thrust him through the chest, ending the fight immediately.