Let's put it this way:
The Giants of 1991, 1992 and 1993 couldn't have beaten the Bills in those seasons' Super Bowls. The only chance they had was in 1990, and they made good on it.
The Redskins of 1991 were much better than the 'Skins of the preceding year and the next two years.
The Cowboys of 1990 and 1991 weren't yet at the stage where they could think about making the SB, let alone win it. Remember, they were 1-15 in 1989.
When OJG says "several" teams from 1990-93 could have beaten the Bills, he seems to be including all four years' worth of the Giants, Redskins and Cowboys in that calculation. I say that the years they won it were the only years they could have won it.
After the Cowboys of '92-'93, the Redskins of '91, the Giants of '90, and the Niners of '90-'93, who else was there in the NFC? The Eagles? Please. The Packers? Not there yet by a long shot. The Bears? They were done. That leaves the Cardinals, Wayne Fontes' Lions, the Vikings, the Suckaneers, the Aints, the Rams, and the Falcons. Any takers? Didn't think so.
The NFC during the early '90s had two dominant franchises each year, a couple of average ones, and a bunch of crappy ones. The distance between, say, the Cowboys and Niners of '92 and the bottom-feeders of the NFC that year was considerable. They had plenty of "off weeks" in their own conference.
Please let's not generalize a couple of great teams into a "dominant conference."