We're putting Williams at LG, where you need the most sand in the pants. LT is where feet and agility matter more than power, so that's the best fit I see for him.
Collins was getting better end of 2017. People were talking pro bowl consideration. People being Cowboy fans, who are admittedly biased, but still. He was clearly improving and up to a respectable level. The Alexander hiring set him back last year. (Proving yet again, if it needed to be shown after the Chaz Green fiasco, that coaching matters, and our coaching hurts our team.)
Colombo got him back on track. I expect him to have a good year. He's probably better at LT now than Williams, but his characteristics are more power over agility (at least of the pass blocking T type), so I put Williams at LT as the better fit.