Serious question: when did we "need a play" from Aikman in the postseason? When was it "crucial that he did so?"
Aikman played in 16 postseason games. The Cowboys won 11 of them (I assume we can agree he didn't make the crucial play in the 5 losses).
Of those 11, Dallas won 6 of them by scores of 34-10, 52-17, 38-21, 35-9, 30-11, and 40-15. Can we agree that there were no "crucial" plays in those games? That leaves 5.
- 1992 NFCCG: Aikman played well, no doubt, but the Cowboys took the ball away 4 times and took an 11 point lead early in the 4th quarter. The '9ers did pull within 4 and the Cowboys scored another TD late. Maybe this one qualifies.
- 1993 Divisional Round: Final score was 27-17, but Dallas had leads of 24-3 in the 3rd and 27-10 in the 4th. It was never close.
- SB XXVIII: The Bills had the lead at the half and the ball to start the 3rd. At which point, Washington returned a Thomas fumble for a TD to tie it. On the Cowboys first drive of the second half, they drove for the go-ahead TD...with a drive that consisted of 7 Emmitt Smith runs and one 3-yard pass on second down (was that "crucial?"). The teams traded punts for a while until Washington got an interception and the Cowboys scored on another run-heavy drive to put it away.
- 1995 NFCCG: The Packers took the lead 27-24 late in the 3rd. The Cowboys took it back on a long methodical run-heavy drive that featured one 3rd-down conversion by pass, so there's one play that I would count. Larry Brown intercepted Favre on the next Packers drive, Dallas scored on two plays and that was that.
- SB XXX: Dallas went up 13-0 early and then the offense did nothing the rest of the game. The only Dallas scores after that came on 2-play drives after Larry Brown interceptions put them right up to the end zone.
So I would dispute your claim that the Cowboys' performance in the playoffs with Aikman hinged on "a very few plays that went in [Aikman's] favor." The Cowboys dominated most of those games, and in the ones they didn't, the defense made most of the biggest plays. I can find two spots that sort of fit what you're saying, but that's it. And I would point to the CAR loss and the 1994 NFCCG as games where they needed plays and he didn't make them.
Again: Aikman was great, not arguing that. It just happens that he was not put in the position in the playoffs where he had to heroball for the Cowboys to win.
Romo didn't have the same dominant team around him, so it came down to heroballing a lot more often. And he did! Dez caught that ball! But, better example: the Cowboys were trailing the Lions in the 4th quarter. Tony led the game-winning drive, which featured a 4th-and-6 conversion and the TD pass on 3rd-and-goal from the 8. He made as many "crucial" plays in that drive as I can find in Aikman's postseason career.
I humbly suggest that your memory of events doesn't really reflect reality.