2: If Darboh is already where Williams took 3 pre-seasons to reach, then you have to assume Darboh's ceiling is higher because his starting point is higher.
A player is a player, using your logic Doug Baldwin should have been cut a few years ago since he was a UDFA and had no real ceiling and was clean up guy at best as far as expectations, kind of like John Randle who never did anything in the league because he was I think a 14 round pick, or Kurt Warner a UFDA that had no ceiling at all, or Dave Krieg who's college doesn't even have football now.
People evaluate players wrong all the time, they look at stats, well stats don't tell you a player was used wrong in a system and his skill set will fit better in what you want to do. Chris Carson is a great example this year as well, nobody heard of him, he was a RB that was used on a passing team and didn't have a lot of stats who learned about running hard after a injury. That passing offense honed his skills in pass protect and receiving however, we are seeing that he learned to run hard. Also how many really good RB's are out there that have shit lines and OC's. This is why we see Pete and John take flyers on guys I believe.
Draft for us is trying to cherry pick the known guys and who we want, our real draft is finding the diamonds still in the dirt that everyone else walks over. That's rounds 4 - 7 and securing the UDFA we have made contact with prior to the draft to lock them up quickly. Roos is another one of those guys.