The lone holdover from Tom Landry's staff is why Dallas became the Legend of Troy. All the ex-miami staff wanted Walsh to start and play over Aikman. Jimmy Johnson however, was always thinking trade with Walsh as he actually tried to move him his rookie year.
Jerry Rhome was a QB guru that Tex, Brandt, and Landry hired for the specific purpose of tutoring and grooming the young legend of Troy (see Jim Zorn, Dave Krieg, and Mark Rypien). Jerry Rhome was a back up QB under Landry until the arrive of a back up QB from the Naval Academy. So Rhome knew the QB position and how to groom young QBs. The fact that Jimmy Johnson kept him even though he made a deal to bring Dave Shula to Dallas as OC in order to get Dave Wannesdat out of Miami (he had signed as the new Dolphins LB coach under Don Shula), shows that Jimmy did respect to most experience coach on his coaching staff.
During staff meeting Johnson had all the coaches comment who should the Cowboys QB between Walsh and Aikman. All the ex-Miami Jimmy Johnson coaches and Dave Shula said Steve Walsh. That is when Jerry Rhome went ballistic asking if they all lost their minds. Troy Aikman was just literally head and shoulders better than Steve Walsh. There was control fighting between Rhome and Shula all year. Shula would be replaced by Johnson in 1991 by Norv Turner. Rhome left in 1990 to be OC of the Cardinals.
Yes Jimmy called Troy a loser but that was not an indicator that he taught Steve Walsh was the long term answer. Jimmy Johnson traded Walsh to the Saints for a 1st, 3rd in 1991, and a 2nd in 1992.The trade to New Orleans would have happen in the 1989 season but Aikman got hurt. 1990 Walsh led the Saints to the playoffs while Aikman sat injured at home again (ironically Walsh knocked the Cowboys out the playoffs the last game of the season). The next year Walsh was beaten out by the Cajun Cannon (Bobby Hebert) and Aikman got injured again as Steve Beuerlein led the Cowboys to the playoffs. By 1992 Troy Aikman was a Super Bowl winning QB and Steve Walsh was a back up about to be cut by the Saints.
Where Troy was concerned, this is a big part of it. Fans have to remember the dynamics of the sale and the draft. The first draft that Jerry and Jimmy had in Dallas, a great deal of that draft was put together by the old staff. Because there was very little time to work with, a lot of what was used was from the old Staff. The Landry Cowboys were going to draft Troy, that was there guy and they had already come to that decision but when the sale went through, that became a footnote. Troy was the best the pick but it is true that there were a lot of people who liked Tony Mandarich from Michigan St. I believe. Sports Illustrated, who was a big thing in all things sports at that time, were puffing his goods like no other. So a few teams had him as the top talent in that draft but some believed, as the Cowboys did, that it was Aikman. Long story short, Troy was drafted 1 and Mandarich was drafted 2, to the Packers I believe.
Jimmy, he believed in competition and pressure. He wanted to insure that the team had a viable option at the most important position on the team and so he took Walsh and I believe he did it because he wanted to be sure. He knew what he had in Walsh and he didn't want to be caught in a situation where he had no options.
I have no issue with it and I'd bet that many years down the line, Troy understands it as well. It all worked out and I have to say that I wouldn't have had it any other way. We all thought Jimmy was crazy some times for the stuff he did but he understood how to create competition and that fear was a driving force in the game. He used it masterfully and it payed results.
That's my recollection of it anyhow.