Spending on a mid career CB has to be the worst ROI in football. Even worse than RBs. All of these guys just fall off a cliff after their big late 20's contract. Nnamdi, Revis, Gilmore, Lattimore, Byron Jones, Diggs, Howard, Peterson, Norman, Sherman, etc.
They all become liabilities and a waste of money almost immediately.
I feel like most positions other than QB, its case by case.
Nnamdi was certainly a bust in Philly. Terrible fit for the defense in Philly but also seemed like a guy who got paid.
Revis was still a great CB, Tampa just sucked. He bounced back big with NE the next season. He was still decent when he retired, just not at his peak level. Could have easily been a solid starter for another couple seasons for contender if he'd wanted.
I certainly wouldn't call Gilmore bad ROI at all, he was a huge part of the Patriots Super Bowl teams. Literally won DPOY for them and was arguably their most important player after Brady. If anything, he's an example of the opposite. Hell, last year in Minnesota wasn't bad, and that was his worst season.
Lattimore has always been vastly overrated. He peaked as a rookie. He hasn't been a difference maker in like 5 years. That was an obvious bad decision at the time.
Byron Jones was always an iffy signing. He was a #2 who got paid like he was a top notch #1. Desperation move that ended as expected.
Diggs is tough to say. I always thought he was overrated as he was SO BOOM/BUST, but he also got paid when he was 25, so I don't know how much that really qualifies, plus injuries have been his issue of late more than play. Hard to predict a 25-year-old is going to suddenly be unable to stay healthy.
Howard was another member of the vastly overrated at the time team. Basically had 1 really good season.
Was Peterson a bad deal? I mean, he was a quality player his entire Cardinals run, and when he left he signed 2 relatively cheap 1-year deals with the Vikings.
Norman was still good for a couple years after his big deal. But the cliff came VERY fast after that, and he was 25 when he got his deal, and was done by 29.
Sherman is debatable. Was extremely important to the 2019 49ers team that was in the Super Bowl, he just hurt his knee after that and then couldn't get healthy and was done in 2 years.
Which brings me to Ramsey. I don't think he's been a bad move for Miami, just not a great one either. He was however, a key player to the Rams 2021 Super Bowl team, so his getting paid was an excellent move for 1 team, and not so much for another. Now at 30, he's still a quality starter in my opinion, but I wouldn't be expecting more than 2-3 years of good play. To a contender, I can certainly see trading a 3rd rounder for that. That would have been a lot better investment for Washington than Lattimore.
I think the recent Surtain/Stingley/Johnson extensions were all good moves. Sauce/McDuffie will be too. Now, guys like Ward, Terrell, or Horn, those feel more likely to bust, and I'd argue Ward is another guy who has been vastly overrated since he went #4 overall.