Agreed that a second contract with the original team is a bit of a rough metric, but to be honest I don't think any very good metric exists. "More than X number of starts" has its flaws too, as a bunch of subpar players were able to pad their "games started" on absolute shit teams like the ones we're all too familiar with from the previous two decades."Second contract with original team" is a pretty rough metric to go by. If I had all the data, that isn't the column I'd choose to use.
"More than X number of starts" might be a good one. Just having a second contract at all might be good too--after all, if you go get a massive contract in free agency, why should that be deemed not a success?
Anecdotally, I think most draft classes have a ton of talent at the top of the second round. Picks 33-40 are usually some of my favorite guys. It's all emotion and no data, but I'd be hard pressed to agree that top of round 2 guys aren't significantly different than round 3-4 guys.
It also needs to take position into account. I can probably find a starting interior offensive lineman in rounds 3-4. I probably can't find a starting tackle, QB, WR, etc.
Maybe some combination of analytical grades and total earnings would be a better indication of how good a player was, but again, not all positions get paid evenly so that has flaws as well.
As for the guys in the 33 to 40 range that you referenced, even if numerous future studs end up being taken in that range, I'd bet that the whiff rate on those picks as a whole is still quite high. Or maybe I'm just jaded from being a Browns fan for almost four decades. It feels like it was just yesterday when we had three 2nd rounders and managed to whiff on all of them.