There are diamonds in the rough and those are the FA players Stephen is looking for.
I agree with what you're saying, but it seems like we're just epically bad at free agency.
Like I get they can't all be winners but last year's biggest success was an aging a back up QB who played about as well as we all though. Honorable mention to Aldon Smith who disappeared after the first 4-5 games, but I wouldn't even really mention him considering how much of a flyer he was.
McCoy an obvious bust that admittedly didn't cost us anything, same about Clinton-Dix, and Poe (Poe did cost us). Cam Erving who was benched week 1 for an UDFA was another bust. Griffen was okay I guess, but obviously traded mid season.
2019- Randall Cobb was ok, but was a down grade from Beasley and Hyder/Covington who gave us nothing. Robert Quinn was a good trade, however, considering he only cost us draft capital and no financial investment, I'd say he's a separate category.
2018- Allen Hurns; bust before the injury. Thompson a 4th or 5th safety until starting this year and getting benched for Wilson, Cameron Flemming/Marcus Martin, busts. Joe Thomas who is a decent 4th LB was the best of the group
2017- Nolan Carrol, Byron Bell, Stephen Paea, were horrible. Damontre Moore I'd compare to Thompson. Good 4th/5th DE. Jonathan Cooper was ok, but was a down grade from Ron Leary. May have been the right decision to move on, however, if your best signing was a guy replacing a departure and they aren't as good, that is part of how you go from 13-3 to 9-7.
I could go on and on, but we haven't really signed a guy that has had a noticeable impact on the team.