What people tend to forget is that Jeff Garcia was recruited to San Francisco out of the Canadian League by none other then Bill Walsh. Then, Bill watched as Garcia went to three pro bowls in a row.
It is a great argument for how good Garcia can be, but an even a greater argument to what was the biggest rift between Walsh and Montana during their time together - that the system (Walsh's) makes the player (in this case, the quarterbacks) rather then the player works the system all that well. Garcia is the ideal guy to run the Westcoast Offense, which the Eagles favor. In Cleveland and Detroit, both offenses were ill-suited to Garcia and it showed. Philadelphia fits his talents like a glove, and with their running game, Jeff can flourish, keeping the ball out of the hands of the opposition. This is a key factor in the Eagles' recent success. Getting and maintaining a lead and keeping their own defense fresh and on the sidelines for extended periods.
Walsh made this type of system, with the right personel, the dominant offense of the 1980's, and the Eagles are showing it still can be effective with that type of player available to run it.