Jason Garrett couldn't win a single game without Romo with a backup QB. Backup QBs who would be released and win games with other teams.
Romo singlehandedly stood this team up for a decade. And what happened when Garrett left? No one wanted to hire him and he could only get a job as an OC, which ended quickly and predictably.
The fact that Romo had a better passer rating despite playing a decade earlier, facing better defenses, and having weaker offensive supporting casts says that they are not virtually the same QB.