It's a heuristic, obviously. Yes, there are outliers and mistakes in every draft. But if you're comparing a first-round pick to a UDFA, you're going to -- in absence of all other evidence -- conclude that the first round pick is MORE TALENTED.
Evan Brown was performing better, but (1) he'd cleared the threshold to be in the NFL for five-plus seasons, and (2) he'd had the experience to know what to do.
I don't think the talent difference between Brown and Adams is huge, even if there was a noticeable production gap at the end of last season.