You seemed to have been questioning Harvin's strength. He could (and did) break arm tackles that would have brought down smaller/weaker receivers. Strength is absolutely a plus in open field running.
Now, if you are focusing exclusively on elusiveness then strength isn't that much of a factor. I'm not even sure how terribly elusive Holliday is as most of his yards are simply finding a seam and evaporating. He has genuine world class speed. (a term used so often to refer to people that don't even have NCAA qualifying times it makes me throw up a little when I hear it anymore) If on the other hand somebody gets a hand on him he's pretty much DRT at 5-5/160.
If you really want a benchmark for elusive in the open field you need to look at Brandon James.