Just for fun, let's walk through this:
The 2007 Cowboys had a worse roster on defense and offense than the 2007 Patriots, and the Pats still lost to the Giants team that also beat the Cowboys by a similar margin.
2009 team let Romo eat 6 sacks against the Packers while giving up 4 TDs to Grampa Favre. Put Brady in there and what difference does it make? Give him 4 TDs and they still lose. But by that pont we're assuming Patrick Crayton turns into Wes Welker or something, and even Brady couldn't upgrade JAGs that much just by showing up.
2010-2013 teams were just hapless. Hell, Romo put up Brady-tier stat lines twice in that period and they still went 8-8.
2014 team is the only one that's close, but it had a worse defense than Brady ever won a title with, and lost a playoff game where Romo had a 143.6 passer rating and 0 turnovers. Hilariously, that's a higher passer rating than Brady ever had in the playoffs. In playoff games where Brady had a passer rating over 95 his record was 17-1. Put him on the Cowboys and it's probably like 2-2 or something.
All of which isn't to suggest that Romo was as good as Brady, just that no one guy could realistically overcome all the Cowboys' problems from top to bottom. Which makes Romo being such a hate sink for disgruntled fans just seem kind of ridiculous.