I was thinking the same. For say a 2nd in 2020 and 5th in 2021, or maybe even 3rd and 4th, I'd absolutely do it. Given Snead's penchant for trading down they would likely turn their 1st rounder in 2020 into multiple day 2 picks anyway. And they have a 3rd round comp. pick coming. Opportunities like this is why accruing compensatory picks helps. if the Rams let Peters and Fowler leave in the spring they will likely net 3rd/4th round comp. picks in 2021 for them.
McVay's past relationship/experience with Williams could be a factor here. Williams has also played 48 fewer games than Whitworth had when they signed him in 2017. So to think Williams could have a good 3 years left (especially given how the Rams manage veteran players) is very reasonable.