It is foolish to try to compare teams from one era with another in the context of how well they would play against each other. The only way to accurately measure (as far as is possible) teams/players from different era is by how well they did against their competition.
A few players could probably play in any era and do well but they most likely wouldn't have the same level of dominance that they had back in the day. Also, the game has changed over the year, in some cases dramatically, so that a guy like Deacon Jones who dominated in the 60s would not be allowed to use many of the techniques that helped him get by opposing OLs (head slap, etc.).
Jim Brown would probably be a very good RB in today's game but he wouldn't dominate like he did in the late 50s & early 60s. With modern training techniques he would be faster and stronger than he was back then but he would not have the size advantage that he had in his era. He played at @ 228 lbs but most DLs were @245-250 and most LBs were @215-230. Going up against DLs who range from 270-330 and LBs who run from 235-255 he would no longer be close to their size and wouldn't be as dominant.
The 1978 Stealers were a great team who dominated their competition and should be judged on that not on how they would play against a team from another era, it just doesn't work. The Stealers were the biggest and baddest team of their era and used that combination of size & strength to full advantage. The 70s Cowboys were just as talented but relied more on skills and innovation than on raw size and strength.
The Stealers advantage in size that they enjoyed in the 70s would be completely nullified going up against the 92 Cowboys. Joe Green was one big, tough guy at 264 lbs (what he was listed at in 1978) but he would be manhandled by the likes of 300+ lb Nate Newton. That's simply too much bulk to give up no matter how good you are and Nate was no fat slouch, he was a massive, talented, and incredibly strong player who dominated the best DT of his day. Can you imagine 250 lb LC Greenwood facing Erik Williams? Williams dominated 290 lb Reggie White so how would Greenwood do against him?
It just doesn't work to compare different era teams against each other head to head.
That said, I do believe that the 1992/93 Cowboys would beat any and every team that has ever existed. They were the culmination of football and had an incredible combination of talent, coaching, size, strength, speed, endurance, and most importantly, depth. Once FA and the Salary Cap came into effect it destroyed a team's ability to build and retain a team with that amount of talented players.
As good as the Patriots have been they would be no match for those Cowboys (or the 49ERs & Bills of those years for that matter) and they are the best the 2000s have to offer.
There may come a time when the game catches up to the early 90s again but it isn't in the foreseeable future IMO.