What does this have to do with Romo starting this year? You can debate his legacy for the rest of time. The answer you're avoiding is the game of football is a team game. I like your lists that you provided. What does Troy Aikman, Bradshaw, Flacco, Brady, Montana, Staubach, and I'll even throw one in Trent Dilfer, have in common? They played with a complete team and a dominate defense. Romo has been hurt by the supporting cast around him. I feel playoff success for a QB is a over rated stat to look at because it looks just at the QB and not at the whole team. The whole team loses games not just the QB and the whole team wins games.
It's not fair to say that Romo isn't clutch when he has the 2nd highest 4th qtr rating in NFL history. He also has the most comebacks of any QB since he became a starter, also his stats are impressive. Has he won in the playoffs or gotten to the playoffs much? No he hasn't but to say that it's his fault alone isn't fair and it's generalizing. The dallas cowboys as a team were not playoff caliber teams.
But to answer your question I would say he belongs in the 2nd group and that's a shame because talent wise he's much more than that but has been hamstrung by bad management, coaching and supporting cast.
This season a healthy Romo is a better QB than Prescott, and I'm a big fan of Dak, go read my other posts about Dak. A healthy Romo is more experienced, talented and savvy. Now as Dak matures, look out NFL, but this season Romo is our best bet, IMO