There is good reason that Gilmore, Jenkins, Haden, etc. are still out there. You want good players vs. known names, regardless of position. That's why adding Wagner would be better than any CB currently on the market.
I would also say that it's March 25th. Free agency started a little over a week ago and we all know there are waves to this. The first wave is past and now teams are evaluating the 2nd wave and who is worth signing ahead of the Draft vs. waiting to see what they can end up with in the Draft first. I am glad the Rams aren't signing someone just to sign someone. Scheme fit matters too.
I would bet the Rams do add CB and or Edge help in the next month. Let's remember that some of the better Rams free agent signings in years past- William Hayes, John Sullivan, etc.- happened in April.